Oil Combi Boiler in Distress... and woman who owns it!

[starkelwood]

Can anybody help with this one!? Until 4 months ago I lived in a bungalow in rural Cheshire with a c. 10 year old Worcester Bosch oil fired combi. I have built a 2-story extension on 1 end (furthest away from the boiler which is in a utility room outside). In the last week or so the pressure has begun to drop from 1.5 bar to 0 in the space of c. 3 hours. No heating/no hot water (boiler won't fire up even after repressurising and resetting with the thermostat override button).
I can find no obvious leaks from the boiler itself. No puddle outside from the relief valve. I can find no obvious leaks from the rad valves or other visible pipework. All of the other pipework is cemented in to the floors. So no obvious discolouration on ceilings in extension. I was also here when the new pipework was installed in the extension and flushed through for leaks etc. There weren't any. This combi was the replacement for a traditional boiler so wasn't built to be a pressurised system. Any ideas before I have to dig up th floor of the entire house!! PLEASE. NB. Very few CORGI registered oil fired heating engineers out here and the 2 I know of are booked up. Thank you.

 

[Kev F]

can you isolate the new bit and then pressurise the old, will find out if its the new part then

 

[starkelwood]

That is one I ashamedly hadn't thought of. Thank you very much. I will go try.

 

[Tibbot]

Can anybody help with this one!? Until 4 months ago I lived in a bungalow in rural Cheshire with a c. 10 year old Worcester Bosch oil fired combi. I have built a 2-story extension on 1 end (furthest away from the boiler which is in a utility room outside). In the last week or so the pressure has begun to drop from 1.5 bar to 0 in the space of c. 3 hours. No heating/no hot water (boiler won't fire up even after repressurising and resetting with the thermostat override button).
I can find no obvious leaks from the boiler itself. No puddle outside from the relief valve. I can find no obvious leaks from the rad valves or other visible pipework. All of the other pipework is cemented in to the floors. So no obvious discolouration on ceilings in extension. I was also here when the new pipework was installed in the extension and flushed through for leaks etc. There weren't any. This combi was the replacement for a traditional boiler so wasn't built to be a pressurised system. Any ideas before I have to dig up th floor of the entire house!! PLEASE. NB. Very few CORGI registered oil fired heating engineers out here and the 2 I know of are booked up. Thank you.

Corgi never dealt with oil, no longer hold register for gas either. Probably expansion vessel faulty and undersized. Your boiler (10 yr Heatlave) could have been installed on open vented system without need for pressurizing.

 

[starkelwood]

When you say the 'expansion vessel is undersized', would this be because of the extension? I had 7 rads in the original bungalow and now have an additional 6 (3 in each room but adding up to the correct BTUs)! And yes, you correctly identified it as a WB Heatslave. If so, can I replace the expansion vessel (or have it replaced) or is it a new boiler (gulp!).

Incidentally, one of those new rads won't heat up at all even though I've been trying to 'train it' by shutting off all other rads and reintroducing thenm slowly. It does work on its own!!

 

[Kev F]

you can add a new vessell on

 

[Tibbot]

When you say the 'expansion vessel is undersized', would this be because of the extension? I had 7 rads in the original bungalow and now have an additional 6 (3 in each room but adding up to the correct BTUs)! And yes, you correctly identified it as a WB Heatslave. If so, can I replace the expansion vessel (or have it replaced) or is it a new boiler (gulp!).

Incidentally, one of those new rads won't heat up at all even though I've been trying to 'train it' by shutting off all other rads and reintroducing thenm slowly. It does work on its own!!

The vessel will be considerably undersized. You will require an additional one (req size s/be calculated) as well as what's in boiler. The existing one should have been checked annually. It may just need attention or replacing. It can also be converted to open vent. Can't be sure of your rad without seeing pipework. Hopefully all 6 new rads are not extending from one old rad.

 

[starkelwood]

Hi and thanks. 1 rad only from the old rads, the rest are on new pipework. The builder didn't check the boiler and the boiler was serviced before the extension was done so I really hope that you have pinpointed the problem.

Interesting about the CORGI point. I've had a fair few heating engineers say they can't look at it becaise they aren't registered for oil fired boilers!

 

[Burnerman]

Which model heatslave is it?
John

 

[starkelwood]

It's a 12/14 which looking at the manual is probably the smallest capacity!

 

[Tibbot]

It's a 12/14 which looking at the manual is probably the smallest capacity!

They'd have to be very small rads if you've 13 off a 12/14. Or the boiler is undersized as well.

 

[Burnerman]

Yes, but a canny old bus they are too!
Expansion vessels are about £70 and the easiest ever to fit - the automatic air vent (brass cylindrical thing under the lid) less than a tenner and also prone to leaking.
I can't comment on the EV being undersized, but if it had failed, the PRV valve would vent to the outside.
John

 

[Tibbot]

I can't comment on the EV being undersized, but if it had failed, the PRV valve would vent to the outside.
John

John. The integral vessel will barely cope with the combined volume of jacket & store let alone another 13 rads & pipework.

 

[starkelwood]

Sorry we aren't expert (at all!) in this field....... We don't have a storage tank if that's what a jacket and store is...

Question - what would be the symptoms if the expansion vessel was too small?

 

[Burnerman]

I can't comment on the EV being undersized, but if it had failed, the PRV valve would vent to the outside.
John

John. The integral vessel will barely cope with the combined volume of jacket & store let alone another 13 rads & pipework.

I completely agree...I've a 12/14 combi in my holiday cot and with 8 fair sized rads it can handle it...but not with additions. Excellent post, ta.
John