Oil usage up after replacing thermal store

[HoneyHaugh]

Hi there, we replaced our Rotex Sanicube thermal store after discovering large amounts of sediment in our hot water supply. It was replaced with a Wocester Bosch unvented 250l cylinder.

The sediment issue was resolved immediately but have noticed a large increase in oil usage. Probably going from 1200l per annum to 2400l.

We have a Worcester Bosch heatslave boiler and underfloor heating upstairs and downstairs serving 2 bathrooms and 4 bedrooms. We were told that the new system should have been more economical. Wondering if we should have replaced with another thermal store or if we need to adjust settings to suit the cylinder.

 

[SJB060685]

That's a large increase. No signs of oil leak? When was the boiler last serviced?

 

[HoneyHaugh]

That's a large increase. No signs of oil leak? When was the boiler last serviced?

Was serviced this time last year, working efficiently. Line was tested and no sign of a leak. Could it be possible that the same sediment that was in the hot water from the thermal store could be in the underfloor heating system?

The increase in oil usage definitely coincides with the cylinder being installed.

 

[SimonG]

Got a love those cylinders with the cold feed higher than than the immersion.

Firstly I would be checking the credentials of who installed the cylinder and get them back to finish it.

Secondly you say you have a heatslave, so a combi boiler? It sounds like you may have an issue with the controls side, but even so I cant see that doubling your oil usage.

Is it only the cylinder that's been replaced?

 

[Chuck]

The sediment issue was resolved immediately but have noticed a large increase in oil usage. Probably going from 1200l per annum to 2400l.

If that is an accurate like-for-like comparison, you have a roughly 13 MW hr excess that needs accounting for.

That amount of energy is enough to heat 220 cubic meters of water by 50°C. So, has your water consumption increased by ca 4 cubic meters per week? If so, you might have a hot water leak.

Alternatively, it's equivalent to having the boiler running 24/7 at an output of 1.5 kW for an entire year.

In my opinion, a likely explanation is that you are measuring the oil consumption over different periods. You can't directly compare a month in winter to the annual total.

 

[snowhead]

Is the property the same average temperature as it was before?
And is the outside temperature on average the same over the year?

 

[HoneyHaugh]

Got a love those cylinders with the cold feed higher than than the immersion.

Firstly I would be checking the credentials of who installed the cylinder and get them back to finish it.

Secondly you say you have a heatslave, so a combi boiler? It sounds like you may have an issue with the controls side, but even so I cant see that doubling your oil usage.

Is it only the cylinder that's been replaced?

I'll have to double check the boiler, it may not be a heatslave as I don't believe it is a combi. Only change was new control and the thermal store (rotex sanicube) being replaced with the cylinder.

The installer was all legit, although seemed a bit clueless as to the increase in oil consumption.
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If that is an accurate like-for-like comparison, you have a roughly 13 MW hr excess that needs accounting for.

That amount of energy is enough to heat 220 cubic meters of water by 50°C. So, has your water consumption increased by ca 4 cubic meters per week? If so, you might have a hot water leak.

Alternatively, it's equivalent to having the boiler running 24/7 at an output of 1.5 kW for an entire year.

In my opinion, a likely explanation is that you are measuring the oil consumption over different periods. You can't directly compare a month in winter to the annual total.

The system has been in place for over a year and we have compared previous years. Relatively mild winter to date and still going through oil. Interestingly during the summer months there is little difference, yet we still use as much hot water so appears to be a heating issue.

There is no loss of pressure to suggest a leak in the system.
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Is the property the same average temperature as it was before?
And is the outside temperature on average the same over the year?

Yeah, all thermostats set to 19 or 20 as before. If anything the winter has been fairly mild to date and still seeing a large increase in oil consumption.

 

[Brambles]

Are you sure that you were running that system on only 1,200 litres / year? Or is the house not occupied all year round?

The UK average annual heating oil consumption is around 2,400litres / year which (I think) delivers just over 26,000kwh.

At 4 beds and 2 bathrooms you are doing well to be running at half the national average!

 

[SJB060685]

Was serviced this time last year, working efficiently. Line was tested and no sign of a leak. Could it be possible that the same sediment that was in the hot water from the thermal store could be in the underfloor heating system?

The increase in oil usage definitely coincides with the cylinder being installed.

With regards to the sediment affecting the UFH i cant really comment, it is a theoretical possibility but i would expect it to affect its function and if is still performing like it was prior to the change then i would assume is ok.
As chuck said above it could be a HW leak, it could be other things.
Is the tank double bunded? And for how long have you noticed this increase?

 

[HoneyHaugh]

With regards to the sediment affecting the UFH i cant really comment, it is a theoretical possibility but i would expect it to affect its function and if is still performing like it was prior to the change then i would assume is ok.
As chuck said above it could be a HW leak, it could be other things.
Is the tank double bunded? And for how long have you noticed this increase?

With regards to the UFH there are definitely hot spots where the warmth is noticeable and other rooms where you wouldn't think were heated. Made me wonder if the thermostats are calling for heat but its not getting there somehow.

The tank is bundled and alarmed. Last winter was when we noticed the increase, 3 x 600l deliveries within a relatively short time. Not much difference during warmer months and then an increase this winter. House was built in 2006 so not as if it's an old farmhouse or similar.

 

[SimonG]

Any chance you had oil stolen?

 

[HoneyHaugh]

Any chance you had oil stolen?

I don't think so, its alarmed for sudden drops. Just going gradually but a lot quicker than before. Hoping to get someone round shortly that will hopefully recognise an issue.

 

[SJB060685]

Good call Si. Yes bunded should be alarmed so you can rule out a split in inner bund
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It could be a whole host of things ranging from oil tank, supply line right through to bad nozzle, disintegrated baffles etc, dodgy stats etc etc etc

 

[HoneyHaugh]

Good call Si. Yes bunded should be alarmed so you can rule out a split in inner bund
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It could be a whole host of things ranging from oil tank, supply line right through to bad nozzle, disintegrated baffles etc, dodgy stats etc etc etc

Thanks guys, appreciate the response. Definitely a link between the increase in oil consumption and the cylinder being installed. Should maybe have replaced the thermal store like for like in hindsight.

 

[SJB060685]

Like I said an increase in fuel could be a lot of things, it's not that none of us haven't experienced this issue but rather there is many possibilities. You said you noticed some of your UFH not coming up to temperature which you suspect is in relation to sediment, this could be a contributing factor which would obviously not satisfy the stat and keep the boiler running longer.

 

[Brambles]

Your issue is nothing to do with the thermal store - albeit, I would get the installer back to correct the defects to make it G3 compliant.