Help! Oil usage on combi

madders07 · 21 January 2020 at 1:16PM

Hoping someone can help identify what's causing this issue or point us in the right direction!

We recently had a Grant Vortex Blue 21kw External oil combi installed.
The settings on this is 1hr of heating in the weekday and nothing over weekends and with the hot water set as 'on' on the controls.

The 650l oil tank was topped up on 20th Dec and it is now down to just under 250l. Trying to work out how we've gone through 100l per week in a 3 bed bungalow with 2 people!

We've had a Grant engineer out today who says it's not the boiler, it's not an oil leak/theft so it must be the controls. However the controls are working fine as the heating goes on and the burner fires up when the store drops below temp.

Any thoughts on next steps?

SD60659 · 27 January 2020 at 5:24PM

With a combi (despicable things) hot water set to on/constant is normal, and your CH preferences are what they are so it's not the demand that's the problem. Even a poorly configured boiler shouldn't use that much oil. How exactly did you eliminate all possibility of a leak or theft? Typically oil lines will be buried (although not very deep) - it's usually easy enough to eliminate a leaking oil tank but the pipework not so easy if it's buried. I would investigate that more closely, but I think it would be a mistake to discount theft entirely. It happens a lot where I live and with times being how they are, people will try all sorts. Nicking oil in the small hours when everyone is asleep is unlikely to disturb, it's a pretty much silent process so unless you have CCTV I wouldn't rule it out. There is no way your boiler is actually burning that much oil with the usage you describe.

Cardew · 27 January 2020 at 7:51PM

Welcome to the forum.

The settings on this is 1hr of heating in the weekday and nothing over weekends

Are you saying that in January you can heat a 3 bed bungalow using a boiler for only 5 hours in a week?

In 5 hours even working flat out the boiler would use 105kWh in a week for heating - about 10 litres of fuel allowing for boiler efficiency. On top of that would be fuel for Hot Water.

Your consumption of 100 litres a week is about 1,120kWh so 160kWh a day.

Now although very high, 160kWh a day is not outrageous for a 3 bed bungalow for heating and Hot Water in December/January, particularly if you like it nice and warm and insulation is not of the highest standard.

Plenty of people on MSE report similar consumption and with gas CH that would cost around £4 a day or £30 a week.

Rodders53 · 28 January 2020 at 7:22PM

The Grant manual is pretty useless but mentions a "36 litre primary store" on the Combis - if that is being kept warm for 'instant' hot water supply? (It's not mentioned in the manual - not that I could find, at least)...
It will also have some frost protection which could operate - depending on area of the UK - with an external boiler?

Whether either could account for such oil consumption I don't know.

How are you measuring oil in the (very small) tank so accurately?

If my Watchman gauge on our 1225 litre bunded tank is to be believed (4/10 left in it) we've just used about 370 litres between 4th December (7/10to date (28th January) - 2 people in a largeish footprint, but modern, house; we are retired so on every day. Grant system boiler, underfloor heating down.

We had water in our original single skin tank and the process of removing the kerosene into drums was noisy (using a petrol powered pump) and also quite time-consuming. (An electric pump would have been quieter but slower, according to the man who did it.)

Help! Oil usage on combi

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