Issues with boiler and central heating.

[DaveR321]

Hi. Thanks for allowing me to register.
If anyone could help me with a few questions, I'd be ever so grateful.
Background;
1. Bought a house, didn't replace pipework but got new boiler. Conventional system, non-combi, tanks in loft etc. Huge gas bills, no real heating.
2. Took the old rads out and fitted new ones except in rooms not needing much heat. Fitted TRVs etc. House now heating up.
3. Boilers cuts out after 30-40 minutes, poor return flow to boiler (possible blockage), overheat protection kicks in.
4. Can't run heating using thermostat/timer/TRV controls. Have to manually turn up thermostat, run for 30-40 minutes then switch off for 1-2 hours.

Questions;
Has anyone come across this before?
Any tips to locate/remove blockage (if that's the issue)?

Pro heating engineers let me down. Plumber has been a saviour but it's still not working. Boiler tested by manufacturer.

When it's a bit cold (like now) but not deep winter, I'm running the heating 4 or 5 times a day for 30-40 minutes a time as that's all I can do. It gets the house from 13-15 in the morning, 14-16, 15-17, 16-18 that kind of thing. Is this about right...?

Many thanks, DaveR

 

[steadyon]

1. Its a circulation issue.
2. Some of the more likely possibilities:
2a. There is an old non-return valve (from a gravity hot water system) causing problems.
2b. There is a genuine blockage somewhere.
2c. It's a one pipe system, and one of the radiator valves is throttled back hard with no radiator bypass.
2d. The pump is failing.
3. About the only way you can find what it is is to follow the heat round.

 

[DaveR321]

1. Its a circulation issue.
2. Some of the more likely possibilities:
2a. There is an old non-return valve (from a gravity hot water system) causing problems.
2b. There is a genuine blockage somewhere.
2c. It's a one pipe system, and one of the radiator valves is throttled back hard with no radiator bypass.
2d. The pump is failing.
3. About the only way you can find what it is is to follow the heat round.

Thanks so much, Steadyon. That's really helpful information.
The pumps are ok, they're new and we checked them. There's almost certainly old non-return valves which can be checked. It could be a blockage. There are two pipes to each rad and I think they are branches off the main supply to and from the boiler.
I'll do as you suggest and follow the heat around. Is there any way to work backwards (?) do you think (forgive me, I'm not very experienced) as the most noticeable thing is the coldness of the last pipe bringing water back to the boiler. I wonder if there was a standard layout to piping in the 1970s so the water leaves the boiler and goes to a,b,c,d etc via all the radiators in a logical way. If the last radiator is hot (properly hot!) but the water approaching the boiler is cold maybe it's at the end of the journey where the issue is. Perhaps it doesn't work like that... I'll go and read up.

Thanks again. I really appreciate the time you spent on this and your helpful reply.

David R

 

[steadyon]

1. Why two pumps. I know it can be done that way but its pretty unusual these days?
2. You can work either way (or both). If starting from the hot (flow) end, feel the pipes going into each radiator to determine where the return coming from a radiator is cold. If starting from the cold end, go round until you find a hot one.
3. The vast majority of hot water radiator based heating systems in the UK are two pipe systems. There is a "backbone" of one flow and one return pipe, usually in 22 mm pipe, sometimes (part) 28 mm. Off this backbone there will be a connection from the flow pipe to the flow side of the radiator, and another connection from the radiator back to the return pipe. These radiator connections are usually 15 mm, but can be smaller. An alternative is where the backbone flow and return each run to one or more manifolds. Each manifold generally supports 4 radiators, but is can be fewer or more. Small bore (often 12 or 10 mm) pipes run from the flow manifolds to each radiator, and another small bore pipe connect the radiator back to the return manifold. Whichever way it is constructed, it is the equivalent of a parallel electrical circuit. I.e. there is a "live" and a "neutral" with each radiator connected across the pair. This way, the radiators share the heat available in the flowing hot water. The system needs to be balanced so that the radiators nearest the boiler don't rob all the heat, but allow sufficient to pass on to be available to those radiators further from the boiler.
4. A one pipe system has a single pipe which leaves the boiler (flow), and goes into one side of the first radiator. The other (output) side of that radiator then becomes the input to the next radiators, and so on. The last radiator on the circuit returns the water to the boiler. There are often balance pipes fitted between the input and output of each radiator to enable some flow to the rest of the system in the event of that radiator being turned off. One pipe systems are much more difficult to set up and balance, and much more prone to causing problems if radiators / pipework is altered.
5. No one in their right minds would install a one pipe system these days, and I think they are no longer allowed under the building regulations. However, the 70's or a bit earlier were probably the time when the two pipe system really took over, so your's could possibly be a one pipe job.
6. Its not that easy to tell which type you have, without access to the underfloor pipework. One either system, each radiator will have a pipe coming up to it, normally one to each end, but sometimes both to one end. Its only seeing how these are connected under the floor that you can tell. However:
6a. If any of your radiators have a pipe running beneath the radiator joining the flow and return pipes, then you almost certainly have a 1 pipe system.
6b. If you have a radiator (other than the last on the way back to the boiler) with NO pipe between flow and return pipes, turn it off. If the radiators "after" that radiator go cold, again you have a one pipe system.

 

[DaveR321]

Hi Steadyon,
I have followed all your advice and exhausted the possibilities, thank you.
There is only 1 pump (I got confused) and it's certainly a 2 pipe system as I took a few floorboards up. I tried following the heat and logically worked from both ends. All the rads were opened up and all of them are hot. I then turned the unneeded ones back to * - 1 on the TRVs just to keep water circulating and a little heat in all the rooms. The Magna clean has been cleaned and I have added Sentinel X900 Filter Aid to the system in the hope of getting more gunk out of the pipes. This morning the flow back to the boiler is good (hot) and I ran the heating for 90 minutes no trouble. Hopefully it's going to be ok.

Thank you so much for all your assistance. Without your advice I don't think I'd have been able to rule out things.

Merry Christmas,

David R