climbing pressure in combi boiler

[shhiffty]

just bought a new house and my combi boiler drips contantly from the ouside overflow. I drain it two or three times daily to reduce the pressure but it climbs again steadily.
I have disconected the filling loop and the problem continues.
The CH and hot water operate fine.
The local water pressure is quite high. Is this something I can fix or is it going to cost me a fortune? Boiler is a SIME friendly format 80e.

[gasman]

There is either too much pressure in the system or the expansion vessle has failed and needs replacing. The correct pressure setting is 1 bar but only when the system is cold and not been used for a couple of hrs. So set the pressure to 1 bar ( when it is cold ) then turn on the heating and watch the pressure gauge if it climbs to 1.5 bar, 2.0 bar or even 2.5 bar as the system gets hot and the heated water expands then this is OK. But if it keeps climbing and goes to 3 bar then the safety pressure release vale will open and dump the pressure out to save the boiler from exploding. If this occours you will need a new expansion vessle fitting.

[gucciman]

you say you've disconnected the filling loop already so two other possibilities:

firstly, the expansion vessel needs re-pressurising, a quick and simple job for a heating engineer. basically the expansion vessel is half full of water and half full of air, the 2 sides being seperated by a diaphragm. the air side is pressurised to about 0.5 - 0.7 bar, the chances are your expansion vessel has lost its air and it needs re-filling. it is very rare for an expansion vessel to actually fail, but the heating engineer can test for this by pressing in the car tyre type valve on the expansion vessel and if water comes out of what should be the air side then the diaphagm has failed and you need a new expansion vessel fitted.

the other option is there is a leak in the water to water heat exchanger (secondary heat exchanger ) and the mains water is leaking into the heating circuit. again quite rare but we did actually have this exact fault on a worcester only last week.

my money would be on your expansion vessel needing repressurising, i would repair this for �50 and include a service on the boiler for that, we do tend to be cheaper than most people though, were in birminhgam if your in that area.

[shhiffty]

Thank you both for your help and time. I think it might be the "leak in the water to water heat exchanger (secondary heat exchanger )" because the bar pressure rises regardless if the heating or hot water are being used - and the filling loop is disconnected - would that be correct? Would that be an expensive operation?
I am in the Dumbarton area, if you know someone who you could recommend.

[lesley74]

Hi

I am curious if you got this fixed. We have the same boiler Sime 80E and we're also having similar trouble. The pressure just keeps building and the hot water is running out of the overflow. The gas engineer has disconnected the incoming water meanwhile while we find a solution. The pressure only rises with the input water for the hot water connected. We do have quite high water pressure which I'm trying to get addressed too with Scottish Water.

We got a new pressure valve fitted, and the problem continues. The gas engineer is thinking it is the heat exchanger at a cost of �200. I'm reluctant to buy a part in case it is wrong. Can anyone offer any advice? I'm in the Greenock area, so not too far from Dumbarton like the other poster!!!

[shhiffty]

hi - i did get it sorted and it was the heat exchanger that needed replaced. I ended up getting a friend of a friend to do it so it didn't cost me too much. He did not think the water pressure was a factor, simply wear and tear

[lesley74]

Thanks shhiffty

We also got ours fixed and it was the domestic hot water heat exchanger. Maybe it's a common fault!