Combi Boiler Constantly Filling Over Pressure

[greg1975]

We have recently moved into a new house with a Worcester 30cdi Combi Boiler installed 2006. The heating and hot water appear to be working fine. We had a Nest thermostat installed and the installer said the boiler pressure was high, about 2.5 bar nearly in the red. As we have taken out a maintenance contract with nPower we contacted them and they sent an engineer who was baffled. He ordered a new plate heat exchange and pressure gauge. Second engineer arrived to fit parts and was also baffled but fitted the parts anyway. The pressure remains high.

Pressing the dump valve handle under boiler at the back empties and reduces the pressure via the overflow but the boiler immediately refills to 2.5 bar. The filler key is removed. Turning the mains water off stops the boiler refilling. Turning the mains water partially off allows the pressure level at which the boiler fills to to be reduced, but that is no good as it also means little pressure out of the other taps in the house. Running either hot or cold tap whilst releasing the pressure works until you turn the tap off at which point it immediately rises again.

I have been told either my hot and cold taps are on the wrong way around! My shower mixer valve has failed! Someone has made a link from the mains water to a radiator pipe in order to fix a leak! I have searched for said link and can not find it yet. Has anyone got anymore ideas before I rip up anymore floorboards? Or do I just ignore the problem as all seems to work ok despite the high pressure, but I don't want to blow the boiler up down the line.

 

[nortonj]

Sounds like your plate heat exchanger is passing to me

 

[greg1975]

That was replaced yesterday and it made no difference.

 

[nortonj]

Ok. There is a link somewhere between your cold main and your heating system, filling loops and the plate is usually first port of call. Can you isolate the cold inlet to boiler? If it still rises then you can rule out the integral filling loop on boiler.

 

[longdogs]

Ok. There is a link somewhere between your cold main and your heating system, filling loops and the plate is usually first port of call. Can you isolate the cold inlet to boiler? If it still rises then you can rule out the integral filling loop on boiler.

+1

Has anyone fitted a new rad and connected to the mains pipe by mistake? I have seen it done.

 

[greg1975]

Yes it still rises when the cold water inlet is isolated. Only stops when I turn the mains water off at stopcock, run a tap, or isolate the CH flow and return but as soon as I turn them back on it rises again.

 

[greg1975]

I have only had the house for a month and no new rads, but before that who knows although the house was empty for several years. I have looked at all the pipes I can get access to in the bathroom and kitchen and no link between the water and radiator pipes. We only have the one bathroom and kitchen and an outside tap. No radiator outside or in kitchen. Boiler is in kitchen. I could pull floorboards up in bed rooms and living room but as they have no taps in the rooms I find it highly unlikely there will be anything but heating pipes.

 

[nortonj]

Turn the cold inlet off to the boiler via the valve to rule out integral filler.

 

[nortonj]

Sorry missed previous post. Could be an old filling loop somewhere that installer left in unfortunately your gonna have to start exposing pipework

 

[greg1975]

Looks like it is back to lifting carpets and floor boards then

 

[longdogs]

http://community.screwfix.com/threads/combi-boiler-pressure.77809/

 

[greg1975]

Plate heat exchanger has been replaced on Tuesday.

 

[longdogs]

Plate heat exchanger has been replaced on Tuesday.

Yeah sorry. I just thought the thread might spark an idea.

Having your hot and cold taps round the wrong way or a faulty shower valve makes no difference. Also, turning the taps on or turning the mains stop cock off whilst filling will affect the rate at which the boiler fills. That's normal.

I'm not an engineer but surely it can only be either a heating pipe connected to the mains or a part inside the boiler passing or mixing the two circuits.

When the filling key is turned off can you physically hear or feel water entering at that point?

 

[St0rmer66]

Old filling loop still connected somewhere. I'd almost bet money on it if plate has been replaced already.

 

[longdogs]

Old filling loop still connected somewhere. I'd almost bet money on it if plate has been replaced already.

So I'm assuming the best places to look for one would be an old airing cupboard or in the loft? I'm guessing it wouldn't be hidden under floorboards?