Combi boiler high pressure problem

[ely_ellis]

Hi all,
I have Glowworm condensing combi boiler at a rented property. The central heating pressure in the system has always been 0.9 cold - 1.1 (max) when running. It has been like this for a few years. I then moved out and rented out the property. Being let, I had to get a gas safety cert last year. I have had a few tenants, but not seen the boiler running hot for about 6 months. I now have a new tenant and while checking the house I noticed the boiler pressure up at 3.2 bar and flashing. As far as I know, the system has NOT been topped up and the internal filler is securely isolated.
The pressure when cold is about 1.2 bar, but when hot at 3.2. I have just bled the radiators and found NO air at all in them. I have drained a small amount of water off and got the pressure down to about 2.8 bar.
Any idea what could be the problem. The radiators are all fitted with thermostats except 2 of them which are permanently on. (heat leaks), and the heat reaches them very quickly, so can rule out any blockages etc.
Could there be an internal fault?
Any ideas please.
Thanks.

 

[dontknowitall]

I'd suspect the expansion vessel has failed. I assume you know that this will take a GasSafe engineer - only mentioned in case you don't. No use asking me any more cos I'm not GasSafe! Hopefully someone else will tootle along soon.

 

[cjg]

same as above, ev looks like

 

[Billy Bob Bob]

ev brown bread (dead)

 

[Reg Man]

As everyone else has said the expansion vessel has lost its charge. May be able to pump it up again if its natural air pressure loss; if not the it will have to be replaced.

 

[ely_ellis]

Well, seems unanimous then.
Just for additional information, the boiler is the Glow-worm 30cxi.
I have been going through the manual and the pressure relief valve is supposed to activate at 3.0 bar, yet there has been no sign of a discharge from the boiler.
The boiler is running fine, it is not shutting down or anything, just flashing 3.2 on the display rather than indicating the CH temperature.
Anyway, just looking for parts now.
As this is on the water side of the system, can a plumber fit this or does this have to be a gas-safe eng.

Thanks all.

 

[Backboiler]

You can get a plumber to fix it without opening the case. He can drain down and fit an external expansion vessel on the return; 12ltr are common

 

[Reg Man]

If you change the vessel which is on the boiler. It will have to be a GSR installer. Why would you risk getting someone who is not GSR to do this work. If it don't go to plan and further work or investigation is required they may have to work on the gas appliance, which means they or you have to get someone who is GSR or they do it illegally. If the plumber works on gas heating systems then why are they not GSR registered? (Incompetent, happy to work illegally, not very good at their job, Not really proffesional, just do a bit here and there)

 

[Backboiler]

If you change the vessel which is on the boiler. It will have to be a GSR installer. Why would you risk getting someone who is not GSR to do this work. If it don't go to plan and further work or investigation is required they may have to work on the gas appliance, which means they or you have to get someone who is GSR or they do it illegally. If the plumber works on gas heating systems then why are they not GSR registered? (Incompetent, happy to work illegally, not very good at their job, Not really proffesional, just do a bit here and there)

External vessel! You do not have to replace the original component in the boiler. Crickey me, It would be easier to replace the boiler than replace some of the vessels on older boilers.
Everyone agrees it must be a fault with the expansion vessel. If the original vessel needs recharging then you need a GS engineer to carry out the work. Anyone with know how can add an external vessel if the diaphragm in the vessel has shot it.
I dont care who does the work, I'm just stating the options.

 

[markproperjob]

yes, fit an external 12 litre expansion vessel off the return pipe somewhere unobtrusive in the house.
very simple job for any plumber, not gas restricted.
a monkey could fit one.
i know, ive done dozens!!

changing the built in vessel usually means demounting the boiler, hence a gas safe chap or chapess needed to diss the gas main.
its perfectly acceptable to leave the ruptured vessel in situ, it will simply become redundant, and fit a new and larger vessel elsewhere on the system away from the boiler. you will still utilise the built in pressure relief valve and filling loop.

now where did i put those bananas?

 

[Reg Man]

Thought my comment would stur the hornets nest.