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!