Help - System losing pressure after oil boiler was replaced

[G M]

Hi folks,

About a month ago, I replaced my oil boiler/burner with a used one that is about a year old. All seemed to be well after it was replaced however, within a week or two, the whole system has started losing pressure - approximately 0.2 bar every 2-3 hours. It seemed to happen a week or so after I bled the rads, but I've gone round every single one of them and I can't see any signs of a leak. I'll explain below what I've tried already.

Checked all rads, removed TRVs to check for any leaks. All good.
Checked expansion vessel located beside unvented cylinder. No loss of pressure (1-bar approx)
Checked expansion vessel for show. No loss of pressure (2 bar approx)
Checked combi boiler enclosure for signs of leaks but all looks ok.
Thoroughly checked all pipework around the house and in the attic (bungalow). Especially checked new pipework where the boiler was replaced. No sign of any leaks.

Things I maybe should check?
Would like to isolate the combi boiler, but there doesn't appear to be any valves installed near it.
The instruction manual says the combi oil boiler has an expansion vessel, but upon checking, it just looks like there is a burner and the boiler enclosure.
One of the bedroom rads was making a small hissing sound which I only noticed yesterday when the heating was on. Thoroughly checked all round the rad and no leaks.

Equipment
Warmflow INDIRECT Unvented Stainless Steel Hot Water Cylinder 150 LITRE (hot press)
Turco Countryman Slimline Outdoor Combi Boiler with Bentone BF1 Burner (outdoor - external housing)
Zilmet 18L expansion vessel (hot press)
Zilmet 12L show expansion vessel (hot press)
4 large, 6 small and 1 towel rail radiators (TRVs on all rads except towel rail)

The system was all working fine for over 2 years before we had the old boiler replaced , so that is why I am suspecting it has something to do with the replacement oil combi boiler. It is massively more efficient than the old one it replaced, but is losing pressure.

I would really appreciate your input/suggestions. Thank you!

 

[SimonG]

What's the installer had to say about it?

 

[G M]

Nothing yet. I can't get the hold of him. Have rang and texted him over the past few weeks. He's always busy it seems.

 

[SJB060685]

Was the whole boiler replaced or just the burner?

 

[G M]

The whole boiler was replaced with a combi boiler. It was an old rubbish thing that was inside the garage. Basically it's on the other side of the wall in an outdoor housing. The different in efficiency is unbelievable. I reckon it is easy 3/4 times more efficient than the old one. Just a shame about the pressure loss. The heat doe have some way to travel with the hour being a bungalow. I can't see how that would be a reason for the pressure loss though.

 

[SJB060685]

Is it a brand new boiler, I thought you mentioned above something was second hand.
Oil boilers that are sealed have an expansion vessel but that is only sized for boiler content and a little extra I was told, often an additional expansion vessel is needed. The volume required is calculated using formula in OFTEC books and many other places I assume and I suspect this might be the problem or not helping. What is the expansion vessel charged to? To check and get an accurate reading you would need to drop pressure out of boiler and check. Also what pressure is on gauge when the boiler is working?

 

[G M]

Thanks for the reply.

The boiler is about one year old and I am told that it was in good working order. It seemed to work ok the first week or two I had it, or maybe I didn't notice there was an issue.

The expansion vessel in the hot press is at 1 bar. I took a reading of this with a pump and initially it seemed low. Certainly below 0.5 bar. This might have been partly my fault because when I checked it a few days ago to see if it was leaking, I left the valve open a little too long and it lost a bit of pressure. I have pumped it back up to 1 bar and it has remained there. I think the expansion vessel is OK in the hot press.

There is a second expansion vessel in the hot press that I assume is for the shower and the pressure on that is around 2 bar. The reading on the vessel states 3 bar maximum, so I think this is OK too. I haven't touched this vessel before, so it has been like that for around 2 years now.

The one thing I have no idea about is the expansion vessel in the combi boiler housing. I don't know how to access it, or even if I need to.

Incidentally, the unvented cylinder is actually 150L capacity. I initially made a mistake in the original post which I have now corrected.

Thanks!

 

[SJB060685]

If you have an unvented cylinder then I'm assuming the second vessel is for that, unless the cylinder had a built in air gap. When the boiler is running what is the pressure on the boiler gauge.
Having a second hand boiler installed sounds alarm bells and you may have set yourself up for endless problems with know access to warranty etc.

 

[G M]

Here's a picture of the boiler specs taken from the actual boiler.

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Thanks for the reply. I'm not sure where the boiler guage is. All there seems to be in the housing is a themostat. The pressure gauge next to the expansion vessel doesn't do anything when I switch the heating on. I've heard that it can sometimes increase significantly when the heat is turned on, but mine doesn't do anything. It doesn't go up or down, except after 2-3 hours or so which is consistent with the pressure loss whether the heat is on or not.

The boiler does say there is a 5 year warranty, but I'm not sure if they will honour this, even if I get a proper service carried out. I'm not the original owner.

The boiler it replaced was a very old piece of junk. It had a service sticker from 1992 on it. I thought a one year old boiler would be significantly better and I got it for a decent price.

 

[SJB060685]

When the boiler is running the pressure will increase slightly but not significantly like you said, unless there is a problem with expansion vessel which is what I was getting at above. If you're sure the expansion vessel is ok (sized properly and charged to roughly .3 - .5 bar under system pressure) then it is most likely a leak somewhere. Have you checked whether the pressure relief valve is sitting properly and not letting by, a bit of muck of something could cause this. I hope for your sake you don't have a split in water jacket around combustion chamber

 

[G M]

When the boiler is running the pressure will increase slightly but not significantly like you said, unless there is a problem with expansion vessel which is what I was getting at above. If you're sure the expansion vessel is ok (sized properly and charged to roughly .3 - .5 bar under system pressure) then it is most likely a leak somewhere. Have you checked whether the pressure relief valve is sitting properly and not letting by, a bit of muck of something could cause this. I hope for your sake you don't have a split in water jacket around combustion chamber

I checked the pressure release valve beside the expansion vessel and it seems ok. I pressed it in a few times and it released water as expected. It actually discharges straight on to the floor and not outside, but that is another story. So far it hasn't discharged any water (except when I did it intentionally).

All the floors are concrete, so if the leak is underground then I have no idea how I'm going to find it. Having said that, the pressure has been solid for over 2 years, until a week or so of getting the boiler replaced. That is why I am highly suspicious there is an issue with it. I need to find some way to isolate it, but there's no valves near it.

Getting a competent plumber in would obviously be ideal, but I'm not flushed with cash right now - a week before Christmas, and it could be very expensive depending how long it takes to find the issue.

 

[SJB060685]

You've got the right idea about isolating the boiler to see if it is the problem. Have you looked all inside the boiler for any obvious leaks? Also have you whipped the burner out (isolated of course) and felt inside to see if theres water inside?

 

[G M]

You've got the right idea about isolating the boiler to see if it is the problem. Have you looked all inside the boiler for any obvious leaks? Also have you whipped the burner out (isolated of course) and felt inside to see if theres water inside?

Thanks @SJB060685 I'm definitely a noob to this, so really appreciate the suggestions.

I've had the door off and felt all round the pipes. I removed some of the insulation out of the way, but everything appears to be dry. I've checked every pipe and joint that I can think of from the boiler all the way through the attic. No signs of leakage anywhere.

I hadn't thought of removing the burner. I'll try that tomorrow. Think there's only a couple of nuts or screws on the front so hopefully it should come off OK. I'll be sure to knock off the mains first as I don't want to burn my face off .

I was going to get the boiler serviced after Christmas anyway, so maybe that might find something.

Is there a section on here to find a local plumber for the service? Thanks!

 

[SJB060685]

If you post your job and location someone might be near you but I cant promise it. A good engineer is for life so it's worth finding someone good, however some might be put off by the fact it was installed second hand. Check what I said safely tomorrow and report back but do NOT fiddle with the burner at all. If you don't feel confident then I urge you to find an engineer. Again if you can isolate the boiler from the rest of the system then that will tell you where the fault is.

 

[G M]

If you post your job and location someone might be near you but I cant promise it. A good engineer is for life so it's worth finding someone good, however some might be put off by the fact it was installed second hand. Check what I said safely tomorrow and report back but do NOT fiddle with the burner at all. If you don't feel confident then I urge you to find an engineer. Again if you can isolate the boiler from the rest of the system then that will tell you where the fault is.

Thanks again @SJB060685 the system lost all pressure this morning. It was at 1 bar around 10pm, then I got woken this morning just after 5am by the banging and rattling of the pipes. I knew right away there was no water in the system. I went to the pressure gauge in the hot press beside the expansion vessel and sure enough, it was at zero. Strange thing is, when I topped up using the filling loop, the pressure very quickly increased to 1 bar. Must have taken 5-10 seconds max. When I top up from, say 0.5 bar to 1 bar, it can take 20-30 seconds at a guess. I don't know if this means anything, but found it rather odd that the pressure increases a lot quicker from 0 to 1 bar than it does from 0.5 to 1 bar, if that makes sense! It seems like it is getting worse now unfortunately. I'll see if I can remove the burner today and have a look inside. Thanks!
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Sorry, just to confirm, it is a condensing Oil Fired Boiler, NOT a combi boiler. Sorry for the confusion!

 

[Best]

Boiler could be leaking inside. But obviously pipes underground could be leaking

 

[Brambles]

I would go back and talk to the vendor of your boiler. It sounds as if the Heat Exchanger on your boiler is leaking.

 

[N plumber]

Hi,

This is not a DIY job, you must consult GSR plumber for this issue.

As there so many criteria to check before come to the conclusion.
It must be leaking somewhere in the system as you need to keep topping it up.

1. Pipe fittings and pipes
2. Pressure relief valve
3. Auto air vent
4. Into the combustion chamber as you can't see this leak as it's run's straight into drain
5. Check your CO detector and ensure its working as combustion chamber leaks give so much problem like light headache étc..
6. Leak in expansion vessel or small expansion vessel
And so many other criteria...

In your case, it must be boiler problem and please seek GSR plumber advice.

All the best and happy Xmas

 

[SimonG]

Tape a plastic bag over pressure relief discharge pipe.

Any pipework under floors?

 

[SJB060685]

So is it a combi or heat only? Your original post said combi and so does identification plate but now you say it's not. Take boiler door off and send a picture of the inside. Does it have a low pressure switch? This should prevent switch live through limit stat and boiler stat to burner.

 

[G M]

Tape a plastic bag over pressure relief discharge pipe.

Any pipework under floors?

Hi @SimonG the pressure relief discharge pipe actually discharges straight on to the floor of the hot press. It's just a grey cement surface and no sign of any water. It is quite warm in there, so I'm not sure if a small amount of water is evaporating before I see it. I've put a small tub straight underneath it now, so should capture anything that falls out of it.

Yes, there's pipework under the flooring. It's all cemented in, so would be an absolute nightmare to get at. Again, the system has been perfectly fine for two years, but only started losing pressure a week or two after the boiler was installed.
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So is it a combi or heat only? Your original post said combi and so does identification plate but now you say it's not. Take boiler door off and send a picture of the inside. Does it have a low pressure switch? This should prevent switch live through limit stat and boiler stat to burner.

Sorry @SJB060685 that was my fault. It is just a condensing boiler. Not a combi boiler. The ID plate confused me somewhat. I spoke with the manufacturer and they said that the unit would be the one that isn't scored out on the plate, but the problem is, the marker has obviously faded, so no way of telling. The exact boiler is this one: Countryman Slimline Outdoor - http://www.turco.co.uk/countryman

 

[G M]

I've had the motor out which was straightforward enough. I'm not seeing any water around, but here's some pictures of the inside with the burner removed.

[automerge]1576670774[/automerge]
I just checked the pressure of the expansion vessel and it has gone to pretty much zero since yesterday. I've no idea if this is expected seeing the system lost all pressure overnight, or if the expansion vessel should maintain it's pressure regardless. No water discharged from the vessel, so not sure where the air went.

 

[SJB060685]

Are those fire boards inside combustion chamber? Is that a hole in pictures 2 and 3? It looks damp on refractory base. If the expansion vessel has lost its charge then you will slowly lose pressure out of PRV when heating at a constant drip. Like I said to check vessel charge it needs to be done when system is drained to get an accurate reading and of course a leak wont help. Every sealed boiler needs a low pressure switch installed and if there isn't one I don't know why

 

[Best]

I've had the motor out which was straightforward enough. I'm not seeing any water around, but here's some pictures of the inside with the burner removed.

View attachment 41892
View attachment 41893
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I just checked the pressure of the expansion vessel and it has gone to pretty much zero since yesterday. I've no idea if this is expected seeing the system lost all pressure overnight, or if the expansion vessel should maintain it's pressure regardless. No water discharged from the vessel, so not sure where the air went.

Your boiler expansion vessel should have air in it. Could be faulty - air valve leaking air or diaphragm inside it ruptured. Needs vessel air charge redone to test.
There is something blocking your burner inside the boiler and it should not be used without an oil engineer sorting it all. Burner could destroy itself as well as burn badly and sooting boiler.

 

[SJB060685]

As Best has said and what I was getting at above. They look like fire boards inside the chamber, these will restrict burner operation, resulting in poor performance and more. The only reason I can think of them being there is to mask a problem. If the vessel diaphragm is ruptured it will fill with water, leaving no room for expansion, the pressure will easily rise to 3 bar and the PRV will discharge, if the valve on top is faulty as well then the same will happen

 

[G M]

Are those fire boards inside combustion chamber? Is that a hole in pictures 2 and 3? It looks damp on refractory base. If the expansion vessel has lost its charge then you will slowly lose pressure out of PRV when heating at a constant drip. Like I said to check vessel charge it needs to be done when system is drained to get an accurate reading and of course a leak wont help. Every sealed boiler needs a low pressure switch installed and if there isn't one I don't know why

Not sure if it's a fire board or some sort of steel bar, but it looks to be part of the unit.
No, I think it must be a particular hot point that is showing a burn mark that looks like a hole. From eyeballing it, I don't believe it's a hole.

Ok, so maybe we're getting somewhere. I let the remaining air out of the expansion vessel with the heating switched off. The pressure gauge directly connected to the vessel read 0. I pumped the vessel up to 1.5 bar this time as per the spec, so both the reading on the pump gauge and the vessel gauge read 1.5 bar. I set a tray under the pressure relief discharge pipe (which goes directly to the floor under the vessel), then turned on the heating system and watched the gauge. I could hear this creaking sound, like a spring. Then low and behold, drips of water on to the tray from the pressure relief discharge pipe. I never noticed any water here before. I was expecting it to gush out for some reason. Does this mean the vessel is faulty? I'm starting to think I might have caused this. About a week after the boiler was installed, I bled all the rads. I made a bit of a balls of it to be honest. Once I bled them, I topped up the system using the filling loop. I never thought anything of it. I bled the rads a second time and made a much better job of it (in terms of heat from the rads). So maybe I did something incorrectly?

One thing I'm struggling to get my head around is the correlation between water and air in the system. When I use the filling loop, I am putting more water in the system I believe, so if there's no leak, where does it all go? When I pump up the vessel with a pump, the gauge moves up as expected, but I didn't add any more water to the system. This is what is confusing me the most. Thanks for all your help so far and I'm sorry for the noob questions!
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Your boiler expansion vessel should have air in it. Could be faulty - air valve leaking air or diaphragm inside it ruptured. Needs vessel air charge redone to test.
There is something blocking your burner inside the boiler and it should not be used without an oil engineer sorting it all. Burner could destroy itself as well as burn badly and sooting boiler.

Thanks @Best I've just posted an update, suspecting there might be an issue with the vessel. Are you saying that the burner is being blocked by looking at the pictures or is this just a possibility? I believe you are local to me so if you want a bit of work if I can't get this fixed I would really appreciate it. Thanks!
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As Best has said and what I was getting at above. They look like fire boards inside the chamber, these will restrict burner operation, resulting in poor performance and more. The only reason I can think of them being there is to mask a problem. If the vessel diaphragm is ruptured it will fill with water, leaving no room for expansion, the pressure will easily rise to 3 bar and the PRV will discharge, if the valve on top is faulty as well then the same will happen

I'm going to call the manufacturer and find out what this bar thing is. I will let you know the outcome.

My pressure gauge did not move upwards at all. It stayed at 1.5 bar, then I heard the spring of the pressure relief discharge pipe and then noticed a few drops of water. I can see the pressure has dropped slightly in the past hour, so the issue is still there. Thanks.

 

[SJB060685]

When you open the filling loop you are adding water from empty yes. When the system is full you are just increasing the pressure inside, yes you're adding a little more water to go from 1 to 1.5 bar for example but its minimal. Even if a system was pressurized to 1000 bar you're only increasing its density slightly. Density and pressure are closely related. The vessel charge should be set to about .2 - .5 bar under system pressure, something has to give in order to accumulate the expansion of water, in this case the diaphragm. If both set to same then the charges fight each other until one gives way by which time the boiler pressure has increased and getting close to PRV setting.
Drain boiler, electrically isolate and recharge vessel to what I said, leave for an hour and check again, from what you've said I expect it to have lost its charge and bingo we have your culprit, or at least one of them. Further more as Best and I both stated, firing that burner up with restrictions is NOT advisable at all, that's another problem that is equally, if not more important than losing pressure.

Edit: have read above comment.
If the vessel is ok after an hour then it sounds from what you just said that the PRV is faulty, they have a spring inside set to a certain force that opens when that pressure is reached. These can fail both ways, not work at all or open prematurely losing pressure

 

[Gasmk1]

does it have a pipe from the boiler going to outside that is dripping if so get the fitter back to rectify the fault

 

[G M]

When you open the filling loop you are adding water from empty yes. When the system is full you are just increasing the pressure inside, yes you're adding a little more water to go from 1 to 1.5 bar for example but its minimal. Even if a system was pressurized to 1000 bar you're only increasing its density slightly. Density and pressure are closely related. The vessel charge should be set to about .2 - .5 bar under system pressure, something has to give in order to accumulate the expansion of water, in this case the diaphragm. If both set to same then the charges fight each other until one gives way by which time the boiler pressure has increased and getting close to PRV setting.
Drain boiler, electrically isolate and recharge vessel to what I said, leave for an hour and check again, from what you've said I expect it to have lost its charge and bingo we have your culprit, or at least one of them. Further more as Best and I both stated, firing that burner up with restrictions is NOT advisable at all, that's another problem that is equally, if not more important than losing pressure.

Edit: have read above comment.
If the vessel is ok after an hour then it sounds from what you just said that the PRV is faulty, they have a spring inside set to a certain force that opens when that pressure is reached. These can fail both ways, not work at all or open prematurely losing pressure

Thanks @SJB060685 that is an extremely helpful post. You've explained that brilliantly. I'm going to find out what this thing is in the burner combustion chamber and let you know. Thanks again!

 

[SimonG]

Hi,

This is not a DIY job, you must consult 'Registered Professional Gas Engineer' plumber for this issue.

As there so many criteria to check before come to the conclusion.
It must be leaking somewhere in the system as you need to keep topping it up.

1. Pipe fittings and pipes
2. Pressure relief valve
3. Auto air vent
4. Into the combustion chamber as you can't see this leak as it's run's straight into drain
5. Check your CO detector and ensure its working as combustion chamber leaks give so much problem like light headache étc..
6. Leak in expansion vessel or small expansion vessel
And so many other criteria...

In your case, it must be boiler problem and please seek 'Registered Professional Gas Engineer' plumber advice.

All the best and happy Xmas

Registered gas engineer is no good for an oil boiler! Unless they do both.
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Was your old system open vented or sealed?

 

[G M]

@SJB060685 @Best I've spoken with the manufacturer and you are both correct. They said no, that fire board shouldn't be there. It's supposed to be in the base of the combustion chamber. What's likely happened is that it has become dislodged in transit. I'm awaiting a response from the installer to see if either I can push it back down into place, or he can come look at it.

On another note, I had the heating system in for a while there (before I found out about this fire board) and the pressure actually increased slightly. I've not noticed any increase in pressure at all since I noticed the fault, unless I manually did it via the filling loop. I'll keep an eye on how much it drops over the next hour or two, then I'll try draining the system and checking the expansion vessel properly. Thanks again!
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Registered gas engineer is no good for an oil boiler! Unless they do both.
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Was your old system open vented or sealed?

It was sealed. The only thing in the system that has been replaced is the boiler/burner. Everything else has remained the same. The boiler it replaced was extremely old and very hard on oil. This new(er) boiler is miles more efficient. Probably 3-4 times more I'd say.

 

[SJB060685]

You should have a refractory base in boiler bottom yes but there seems to be fire board on all three sides of chamber, like I said the only reason I can think of is to repair or mask a problem. Do your checks and let us know in an hour.
PS. You've mentioned several times about how much more efficient it is but I'm willing to bet the guy who installed it probably didn't commission it properly either, you might find theres more to be had yet but this requires an engineer.

 

[G M]

You should have a refractory base in boiler bottom yes but there seems to be fire board on all three sides of chamber, like I said the only reason I can think of is to repair or mask a problem. Do your checks and let us know in an hour.
PS. You've mentioned several times about how much more efficient it is but I'm willing to bet the guy who installed it probably didn't commission it properly either, you might find theres more to be had yet but this requires an engineer.

Thanks @SJB060685 I don't know if I'll get it done in an hour. It's absolutely lashing outside

Yes I'm sure you are correct about the efficiency. There's probably more to be had. For example, there's no insulation on any of the pipework. I'm sure that doesn't help. There's also a giant hole where the old boiler flue was. It has been very much patched up. There's a small run of about 3-4 inches of copper pipe from the back of the boiler house to the garage that is exposed to the elements too. None of this can help the efficiency surely.

Yes, sorry to keep banging on about it, but we didn't realise how rubbish the old system was. It cost a clean fortune to run the heating system. Once we get these issues sorted, I plan to put insulltion round all the pipes at least from the outside, into the garage loft until it gets to the house wall (it's an attached garage). None of the pipes are tied down either, so they rattle around a lot and they are very easy to lift. I'd like to secure them somehow, but all that will come later.
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Ok, so I've inspected the boiler again and it seems that part of the surround has come loose. I've pushed it to the bottom for now, so the top is a bit exposed. Not sure of the short time significance of this, but guessing I'll need to secure or again to the top somehow.

Incidentally, the pressure has dropped rather fast from 1.5 bar to about 0.75 bar in the last 1-2 hours. Not sure if me messing about with the oil burner has made this worse than normal.

I'm going to drain the system later today if I can and do as @SJB060685 said about checking the vessel. Thanks!

Roof of combustion chamber:

 

[SJB060685]

For now let's just find the cause of the pressure dropping without the boiler running. The boiler is something you need to get an engineer out for, I appreciate this close to Christmas you don't like that idea but from what I can make out from what little I can see in photos it shouldn't be fired up.

 

[G M]

For now let's just find the cause of the pressure dropping without the boiler running. The boiler is something you need to get an engineer out for, I appreciate this close to Christmas you don't like that idea but from what I can make out from what little I can see in photos it shouldn't be fired up.

Thanks. I don't think I'll be able to do without the boiler over Christmas with the sub-zero temperatures we're getting, but if it does fail then I'd be expecting some help from the installer. I have emergency home heating cover with my home insurance in case it does fail completely. I'll let you know how I get on with draining the system. The pressure has almost dropped to zero now. It has dropped very rapidly in the past few hours.