Boiler Losing Pressure

[tonyathome]

I have a Worcester Greenstar HE25 combi boiler which is losing its pressure on a weekly basis.
I have checked every foot of the pipework and there are no leaks, but the pressure drops to 0 within a week of filling it up. The boiler is 5 years old and has never had any major problems.
Any ideas would be appreciated

 

[gas4you]

Checked the prv discharge pipe out side? Is it dripping constantly?

Tape a plastic bag over it to check.

 

[landyandy]

What pressure are you filling it up to?

Andy.

 

[methaneman75]

is pressure rising sharply when heating is on, if so its the expansion vessel, plenty links on this site how to fix.
If not ,to determine properly where leak is shut off flow and return to boiler for a day or so and monitor pressure, if no loss during this time leak is on pipework. Only problem is you wont be able to use ch during test time only hw which is not good at this time of year

 

[bengasman]

If you have really checked every foot of pipe, there are only 3 things left; the boiler, the valves and the rads.
I am disregarding the possibility of someone stealing the water.

 

[tonyathome]

Filling it up to 1 bar as per the manual. When the heating is on it rises to about 1.5 bar on the indicator on the front of the boiler.
Havent checked yet to see if there is a constant drip outside. I have a feeling from reading elsewhere that it could be either a faulty pressure release (which I will check tomorrow) or expansion vessel.