Biasi M90E 24S combi - Loosing pressure

[Binghams50]

Hi all was wondering if somebody could assist with a problem I have with the above boiler?

Approx 4 weeks ago I noticed the laundry was getting very warm which was of concern especially given that we have not been using CH? Kept my eye on it and found that the boiler was firing up un-necessarly, shutting off then coming back on again when there was no call for HW or CH. The boiler must have been red hot given the heat in the laundry.

I am not concerned about this as its probably HW sensor which is common problem and will get an engineer out for this.

My boiler is always switched off now other than bath times / CH is needed and have noticed that it only looses pressure when used? Boiler was on for 4 hrs and lost about 0.5 bar (normally at 1.3bar). felt under boiler and no obvious leaks?

Could the constant firing up have cracked the heat exchanger? Also confused that does not leak when off / system cold?

I have changed all the rads and pipework in the house over a period of 3 years so am concious of keeping my eye on the pressure and it as never previously lost pressure. The only plumbing carried out of late was removing hall rad for decorating behind? I am confident that I have not spring a leak as no signs in and around house, obviously cannot check under ground floor but holds pressure when not used / system cold?

Thanks in advance

Deano

 

[plummerman]

The central heat thermistor also controls frost protection, thermistor drops out of banding the board then thinks its freezing and fires the boiler up to protect it.

Have you checked the expansion vessel charge? Or poked ya finger in the end of the prv pipework to check if it's been drippin etc?

 

[Binghams50]

Have not seen any signs that the overflow has been leaking and have only noticed pressure dropping when there has been a call for CH in the past week given the cooler weather hence have been switching it off?

The boiler has been firing up and shutting down for at least a month without loss of pressure until CH was used in last week?

Cheers

Deano

 

[Binghams50]

Hi Plumber man,

swithched the central heating on last night after my last post and found that the pressure went upto 4 bar and the PRV blow off started to drip! never noticed this pressure increasing before or the drip.

Deano