Pressure drops when CH Hot but not when cold

[aroundM21]

(Worcester Greenstar Jnr 28, 2.5 years old. Bizarely the PRV pipe (far right) came away yesterday but NO water has come from of there)

Why would my system loose pressure when the CH ring is Hot, but not when it is cold ?? (I realise Hot shows lower pressure level than Cold).

I've tried combinations of closing different Rads with no noticable difference. It always looses pressure (1 bar drops in 60-90 mins) if the CH thermastsat control is demanding, and the Boiler has Rad symbol on.

I thought it must be a leak in the pipes (ie boiler internals OK) but surely it would always loose pressure irrespective of temperature ??

Appreciate if this could help me identify my problem. Needle in a haystack !!

Mike / Manchester

 

[ScottishGasMan]

Loosing pressure when hot can be because of expansion in the suspect area of the leak, Ie: a bad joint may expand exposing a small leak when hot.

some greenstars did have an issue whereby the main heat exchanger cracked internally and leaks being un noticable as the water is either evaporated or runs down the condensate pipe.

I would be inclined to get under the floor and watch the pipes if possible, or get an RGI to get a look at the boiler.

 

[Andygasman2010]

some greenstars did have an issue whereby the main heat exchanger cracked internally and leaks being un noticable as the water is either evaporated or runs down the condensate pipe.

Was this problem on the CDi heat exchanger only? (the square one) The Junior uses a differnt kind which i've not had any problems with personally.