Problem with Potterton Combi Boiler Help and information on all topics relating to your central heating, air conditioning and ventilation issues.

[sutton_blue]

Hi, I have a 'Potterton Performa 24 Eco He' which I had fitted about 3 years ago to a system that was in place 14 years ago when I moved into the property. The system has no external room thermostat and controls off the 'central heating temperature control' on the boiler. The problem I have is that when the boiler starts up from cold in the morning it heats up
fine and cuts out when it reaches temperature, then when it calls for temperature again it keeps cutting in and out until I guess it gets back up to temperature and then switches off. I have noticed when cold the pressure guage reads '0'. When running the higher I turn up the temperature control the higher the pressure goes until if I turn it up high enough it starts to go into the red on the gauge. I tried fitting a room thermostat, on someones advice, the thermostat worked fine but then when I turned up the boiler control so the pressure gauge climbed up into the red. The manual advises that the temperature control on the boiler be set at maximum during the winter but this will clearly put the pressure in the system up and lift the safety valve. Does anyone have any ideas on what I can try next short of calling in an engineer.

The hot water works fine.

Thanks in advance for any replies

[htg engineer]

Expansion vessel faulty, sometimes possible to re-pressurise but may need replacing.

Get an RGI out to repair.


htg

[sutton_blue]

Thanks for the reply 'htg engineer'.

I have taken off the front cover of the boiler but can't see the expansion vessel, I was going to put a gauge on it to check the pressure, but it looks to be behind a panel at the back with no means of access short of removing the boiler from the wall.

According to the manual, to replace the expansion vessel, the boiler has to come off the wall, is this also the case for checking the pressure in the vessel? if so it looks like getting someone in.

Thanks again for any replies.

[sutton_blue]

Back again!

Managed to locate access to the shrader valve on the expansion vessel, there is an access panel on the top of the boiler behind where the flue comes out, couldn't see it first time for dust. The vessel was empty of air and luckily water, replaced the valve and repressurised to 0.5 bar. the system is now working correctly maintaining a working pressure of between 1 to 2 bar depending on where the boiler temperature control is set. I have fitted a room thermosat and set the boiler stat to nearly maximum. The problem I still have is that the boiler cycles in and out every few seconds once it calls for heating when hot, when it first starts up in the morning or from cold it runs fine.

Can this be down to poor flow through the system (all the rads work fine, no cold spots) the manual says that the pump setting should be on 3 but there appears to be no speed control on the pump which should be on the cover of the electrical terminal box of the pump. I also notice from the manual that there is a safety thermostat and a temperature sensor on the flow pipe, could these be faulty. I may be clutching at straws here.

Any advice would be much appreciated.

[htg engineer]

You can normally get into the schrader valve to check the pressure - have another look. If you don't want to remove the boiler from the wall or if want to do it yourself to save abit of money - tee into the return close to the boiler and fit an external pressure vessel (they're cheaper than manufacturers replacements too) ideal if the boiler is somewhere discreet (like a basement or cupboard) so having an external pressure vessel wont be in the way.


htg

[htg engineer]

If you press the schrader valve and get water - the diaphragm is shot.
There should be air in that part of the vessel.

htg

[sutton_blue]

Think I worded it wrong, I mean't to say that there was no air in the expansion vessel and no water.

Thanks anyhow for replying.

[Steve the gas]

Hi,

The ex vessel pressure should be about 0.8 bar.