Pressure in combi keeps going up (moved from forum info)

[MGB69]

I have a baxi main 30he combi boiler and yesterday I took the secondary heat exchanger out of the boiler to clean it because the shower kept going hot then cold and many threads have said this would be the cause. Cleaned up great and put back in to the boiler however the pressure gauge goes up and after about 2 hours is at 3 bar and the pressure switch kicks in. The water feed to fill the system is disconnected so it's not that can anyone help as to possible causes and potential fixes. I have read that it could have something to do with the expansion vessel could this be right if so is there anything I can do. Any help greatly received

 

[Cgas]

Have you been having the heating running or is it filling up when the heating is not on? What did you clean the plate with? Did you try and ram screwdrivers or something into it ?

 

[MGB69]

It is going up with the heating off. I cleaned it with chemicals and didn't put anything else in to it to clean it.

 

[picasso]

Another filling loop somewhere on the system or you have piholed the plate when you cleaned it.

 

[hertsboilers]

What chemical did you use for heat exchanger cleaning? Might it have caused pin holes?

 

[MGB69]

I used drain/limescale cleaner basically caustic soda

 

[Madrab]

Oh Dear .... I believe the Main's primary heat exchanger is aluminium, I am sure more experienced chaps can confirm.

If so then unfortunately you could have pinholed the primary heat exchanger, caustic soda and aluminium are energetic besty friends.

 

[DP]

Ran, is it a plate to plate heat exchanger or something else?
Have not seen a P2P made of anyother material but that means jack 5hi7e

 

[MGB69]

Oh bugger!

 

[Cgas]

New plate it is

 

[Agile]

A hole in the plate HE is only one possibility.

If you can work out how then you can pressure test it out of the boiler.

Tony

 

[I Like Sleeping]

Turn off cold water supply too boiler see if it stops pressure increasing