Potterton promax losing pressure?

danfitzjohn · 8 Feb 2021

Hi all,

Got a 3 year old potterton promax that seems to lose it's pressure every 6-8 weeks particularly in the colder months. First we note no hot water, check gauge which is on zero, than I turn a grub screw (don't know what it's called) to increase pressure (which normally goes too high) and then i bleed the radiators to get the pressure down to where it should be approx. 2 bar where it works fine for a few weeks longer

Any ideas why this happens and what can be done about it?

Many thanks !

ianmcd · 8 Feb 2021

when the heating has been on for half an hour what does the pressure guage go to ?

danfitzjohn · 8 Feb 2021

It's currently on now and at 2

CBW · 8 Feb 2021

Check the copper pipe if it terminates outside for any water evidence.

danfitzjohn · 8 Feb 2021

Yes there has been water coming from there..

CBW · 8 Feb 2021

Expansion issue, prv seating issue or both. For the former it will require a gas safe registered engineer.

terryplumb · 8 Feb 2021

When your system is cold ,set the pressure to 1 bar. If the pressure does NOT go above 2 bar when central heating has been running for an hour or so ,and water is dripping out the copper PRV pipe outside ,your PRV needs replacing. Do not confuse the pipe outside with a plastic pipe ,which is for the condensate ,and dripping from that is expected under normal boiler operation.

danfitzjohn · 8 Feb 2021

Many thanks, I’m not sore what a PRV function is but would a faulty PRV also be a reason for the system to ‘lose pressure’ every 6 weeks or so?

terryplumb · 8 Feb 2021

Pressure relief valve ( PRV). When water is heated it expands and increases the pressure in your sealed central heating system / boiler. You have an expansion vessel ( EV) that accommodates this expansion. If it is not functioning as it should ,the pressure will increase to 3 bar ,at which point the PRV will open and allow water out to drop pressure. If the PRV is faulty / not fully closing and allowing water to drip out ,when system pressure is way below 3 bar ,it needs replacing.

danfitzjohn · 8 Feb 2021

Many thanks for the response. Is there a possible different reason that the system loses pressure over time and anything I could check.

terryplumb · 8 Feb 2021

As you have told us that water is dripping from the prv Pipework ,that's the first thing to sort out.
Do as I suggested earlier. Set pressure to 1 bar when cold. And monitor the PRV pipe outside.

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Potterton promax losing pressure?

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