Problem with low and high pressure in Potterton Performa 28i

Hi all,
First post for me here and ive done lots of looking around the forums for a solution to my problem with the boiler.
I brought a new built house around 5 years ago with a new Potterton performa 28i Combi boiler.
A few years ago i noticed that the pressure was going down to 0.5 bar when the heating was off and when the heating was on it was going over 3 bar.
At the time I had BG cover and they came round and said expansion vessel was faulty and went forward with replacing it. When they came to replace it they said they found lots of sludge in the system so it would need powerflushing. Once I got their extortionate quote i did some checking and saw that they recommend this all too regularly so I pressed this with my builder and they agreed to come and put in new inhibitor into the system. So i didnt go for the powerflush in the end.

Well to this day I am still getting the problem and because the hot water and the heating seem to function ok I havent done anything more with this.
However I just had a recent boiler service done and explained the problems to the engineer and he again mentioned powerflushing would fix this problem (not a BG engineer before anyone asks).

From my searching it does not seem that powerflushing is meant to fix issues with highly variable pressures and as my expansion vessel was replaced two years ago I think that should be ok.
I tried my heating last night and it went to almost 3.5 bar and i went to the release pipe expecting water to be coming out but there was no water being expelled which i would have expected and which would have accounted for the lowering of the pressure once the heating turns off.

I have had to add water to the system over the past few years to put the pressure up and the engineers have told me this could go long term problems if done too frequently.

So my question to anyone that may be able to help is what could be wrong and would the sludge in the system (if it is heavily sludged again) create problems with high pressure not being handled correctly.

I don't want to spend £400 on a powerflush only to find out that the PRV or the expansion vessel need to be rectified. But now that two engineers have said this I am being led to believe that powerflush is my only option. Except i don't know if this is too just drum up business on my expense......

If any powerflush experts out there could allay my fears about this it would be great......

Please please help....I am at the end of my tether trying to fix this.......

The expansion pipe is blocked not allowing the new? (how old is it now) expansion vessel to work or the new vessel is also kaput.

If your system is badly sludged then it needs cleaning preferably by powerflushing. Just adding inhibitor to the system is useless.....like adding clean oil to a gunged up engine.

Try fitting an external expansion vessel (how many rads on your system...lots may mean your internal one isn't enough)....then get the dam thing cleaned.

Thanks for the reply...

I've got 11 single rads in the house....is the performa 28i enough for this?

How much would an extra expansion vessel cost to put in place? and would it need to be done before a powerflush or could it be put in place later?

It's not the boiler thats the issue it's the size of the rads and water volume......water expands as heated so if the air pocket isn't big enough to hold the expanded water pressure will rise.......11 sounds a lot so it maybe just adding an external one will do......cost 40 quid for the vessel 60 quid to fit est.

Flush before preferably....

powell30 said:

The expansion pipe is blocked

Click to expand...

Wow that's a 22mm pipe!