DIY Doctor UK DIY Forums

Hi I have a Potterton Performa Combi boiler approx 6 years old, regulalry serviced. Probem is I keep losing pressure when the central heating is run, no issues on hot water only.

The wife had the central heating on for a couple of hours yesterday and the bolier lost nearly half a bar. Normaly have it set at 1.5 when cold

I have checked all my bleed valves, connections, drain taps etc for leaks and cant see any problems.

Where can the problem be, is is the boiler, the pipework? please help got 2 young kids and i need the heating on.

Mnay thanks
Tony

With the heating on, does the pressure rise to above 3 bar?

Check PRV discharge, any leaks ?


htg

Pressure/expansion vessel may need pumping up or the diaphram may be split.

Cheers

I can say i have checked what the pressure is when the boiler is producing hot water and central heating, i will have a look. As for the PRV seems to have collected some water from it, about 1inch in the bottom of a coke can.
How can i check the pressure/expansion vessel or if the diaphragm is split?
Regards
Tony

FURTHER UPDATE
Wife says heating has been on for 1hr, pressure is just over 2bar. When the bolier fires up the pressure goes up until is turns off and the reading is now 2.6, (in to the red zone) maybe why i am getting water from the PRV, but why is the pressure rising so much and into the red. Normal cold pressure is 1.5bar

Thanks
Tony

Try re-pressuring the expansion vessel. Release pressure from system, using a foot pump, pressurise to 1 bar.


htg

Thanks HTG for your reply.
Maybe silly question to ask but how do i re-pressurize the expansion vessel, where do i connect the foot pump and do i use the pressure gauge on the pump for reference?

There'll be a schraeder valve on the expansion vessl (like a car tyre) connect foot pump, and pump to 1 bar (on the foot pump gauge) then refill system.

If there's any water when the schraeder valve is pressed, the expansion vessel needs replacing.


htg

Guy's I will try and pressure the expansion vessel and see if there is any water in it. I will let you know.

Whats the average cost to replace the expansion vessel if needed?

Regards

Tony

Hi HTG,
I released the pressure from the boiler by twisiting the PRV until the gauge said zero, i then repressurised the expansion chamber with a foot pump as your suggested to 1bar and repressuresed the system. Boiler is working fine, pressure seems constant and with no loss. I will continue to monitor and hope the issue is resolved, if not I will be back on.

HTG engineer many thanks for your help, it has been invaluable.

Regards

Tony

Glad to be of some help.

Thanks for letting us know the advice worked. We get many posts, where we give advice then never hear anything else - we can only assume our advice worked and that's why they've never been back.


htg

Sorry missed the bit about the cost of replacing the vessel. If you go for the manuafcturers pressure vessel, sometimes you have to take the boiler off the wall, and can be expensive. But you can buy an expasnion vessel and fit it externally (tee'd into return, near boiler) which is alot cheaper and simple a DIY task (£30 - £40ish)