Worcester Bosch 350 loosing pressure mystery

[Fernville]

The boiler is 14 years old. Over the past couple of days has started loosing pressure. From topped it up to 1 bar it fails to low pressure in 2 days. There are no apparent leaks. It seems illogical the small bore piping has sprung a leak after all this time but the boiler does not seem to be leaking either. None of the radiator valves are damp or show signs of staining. I am reluctant to spend money on repair if this is the first stage of failure.
Where should I look to see if it is boiler or system failyre.

 

[gasmarc]

it could be an internal leak but an easy way to prove its the boiler is to isolate the flow and return under the boiler and dont use it for 24 hour good luck

 

[Fernville]

Obvious and very logical. Shows my early stages of senility. Thanks will let you know. I will turn off the boiler gas supply to be safe

 

[washer]

Your brave, I wouldnt touch Worcester isolation valves, they always leak!

 

[Billy Bob Bob]

i also would leave the isos well alone,they will leak so you are looking for a logical answer ,check the external pressure relief valve 15mm pipework running/staining???? expansion vessel and probable prv failed logically speaking of course you need new parts sarcasms free advice is chargeable

 

[gasmarc]

well I never touch isolation valves unless it is unavoidable as they sometimes leak

 

[Fernville]

Taking the case of I can now see the pressure relief valve dripping only when the central heating is on and the pressure reaches 3.5 bar.
What is the 'normal' high pressure. I know the low/cut offf pressure is 0.5 bar anr the normal setting when cold is 1.0 bar

 

[Fernville]

Thanks for your help gasmarc it is now solved. The small tray under the controls was storing up the leak and it all came with a rush. When I took this off the was a very slight leak from the PRV when the pressure got up to 4.0 bar, far to high. Guess this will be the expansion tank at £200+ Ahh well a new boiler it owes me nothing. Thanks guys

 

[CES]

If its the expansion you could always try and reinflate it, or cut another one into the system.

 

[gasmarc]

it will be much easier to replace the vessel or as above cut a new one in