Potterton Promax combi HE Plus Pressure Dropping

Lizk2309

Hi,

Looking for some advice please.

I have a Potterton Pro Max combi HE Plus boiler that is about 7 years old. Recently the pressure has been dropping every day and needing topped up to get heat/hot water. I top it up to around 1 or enough for the error to go away and then we have heat hot water again. When I put the heating on the pressure is rising to 3 nearing the 4 and then drops again when I turn the heating off. I located the pipe outside and put a bag over it, it’s now filled with water....I’m guessing this isn’t right?

Can anyone please advise, total novice here

Browntoa

The pipe outside is a condensate outlet , it's meant to drop water and should not be blocked up .

Are there any obvious signs of a leak from the boiler underneath ?

Any wetness under radiator anywhere indicating a leak ?

Some 1970's houses had the copper pipe placed under the concrete floor unlagged , the concrete attacks the pipework causing pinholes.

Lizk2309

Can’t see any leaks around any of the radiators. When I turn the valves to bring the pressure up again the right valve leaks a small amount of water. It doesn’t leak at any other time.

The house is 7 years old.

thorganby

It is nothing to do with condensate.

The reason that the pressure is dropping is because the expansion vessel inside the boiler has failed or simply needs re-pressurising.

If your system pressure is rising above 3 bar towards 4 bar, the pressure release valve will operate discharging into the pipe outside that you have put the bag over, allowing the system pressure to drop.

The expansion vessel has a diaphragm with water on one side and air on the other, and the air side should be at a pressure of 0.5 bar.

If when the pressure is checked water comes out of the Schrader valve, the diaphragm has failed.

If no water comes out it needs re-pressurising to 0.5 bar.

If you can't check the expansion vessel yourself you will need to call someone out who can, as this pressure dropping cycle will repeat.

Lizk2309

Thanks for your response, way too complicated for me. I’ll get someone out to look at it. Roughly how much would it be to fix this? Any idea?

thorganby

Lizk2309 wrote: »

Thanks for your response, way too complicated for me. I’ll get someone out to look at it. Roughly how much would it be to fix this? Any idea?

If the expansion vessel simply needs re-pressurising, I would think that it would just be the call out charge.

If the expansion vessel needs replacing, it would be the cost of this item for your boiler plus the labour charge to fit it, which may vary widely depending on your location.

Hopefully it just needs to be re-pressurised.

Lizk2309

Thanks for your help. Appreciate it.

JohnB47

Just to add to thorganbys post, which I believe is correct.

I am not a plumber but I've repressurised my own systems expansion vessel and found that it fixed a similar problem.

You, however, will probably have a secondary problem, because your systems pressure release valve has vented (mine didn't).

This means that dirty water will have passed through the release valve and some dirt/grit may have become trapped in the seal, making it impossible to re-seat properly when the pressure reduced.

It's a common result of a problem like yours, so your plumber will probably replace the valve, as a matter of course, as well as repressurising the system.

The valve isn't expensive - I searched and found ones for your system selling for around £9 but who know what a plumber would charge for supplying and fitting one.

By the way, I know "Energy" might seem the best place but your post probably would have had more replies if you'd posted in on the "In My Home (Includes DIY)" section.

Lizk2309

Thanks for the info, I took the casing off my boiled last night because I was going to have a go at fixing and wanted to see if it looked possible but I couldn’t find a pump maybe I’ll just get a plumber to be on the safe side!