CH LEAK.?.??

[Crakkers]

Hi boiler pressure drops more often now.

I have done a leak test on the rads and they appear fine. When ch comes on the pressure guage shows normal to high. When switched off it drops low and sometimes to zero. This prevents ch comming on. It only takes a day or so before I have to top it up via the filler loop. It takes very little water to fill it.

if the problem is with the boiler, what can it be and how do I find out??

cheers

Crakkers

 

[footprints]

First port of call!
Check the discharge pipe (open ended piece of copper tube outside)
Either it is leaking all the time with a slow drip, or discharging in a rush as the system heats up.
The pressure when cold should be around 1bar rising gradually to maybe 1 1/2 to 2 at most as the system heats up.
If the pressure rises rapidly to around 3bar and the discharge pipe vents the problem is with the pressure vessel.

Mind the venting water it is very hot!

 

[Crakkers]

Hi

Done as suggested, no water comming from outlet.

Pressure dropping quicker and quicker now when CH is not on, when on pressure goes nearly into the red.

Why such variance???

Crackers

 

[footprints]

It sounds like you may have two problems, that's not unusual ,I sometimes think that's why they call 'em combis, because often as not more than one thing goes wrong !

The pressure vessel is suspect, it is a container with a diaphragm in the centre, one side is air under about 1 bar pressure the other side is the water system, as the water heats it expands pushing on the diaphragm and compressing the cushion of air. The pressure in the system remains fairly constant. If the cushion of air is lost the whole cylinder is filled with water there is nowhere for the water to expand to so the pressure rises rapidly.
Normally this results in the discharge valve venting to outside. However you may have leaks on the system as well, as you say it requires very little water to repressurize, so you only need to loose a tiny bit to return to 0 pressure. Check rad valves and joints for small leakage you may not find them wet but look for brown staining or white deposits from scale.

 

[Agile]

Telling us the boiler model would help!

What you have told us is not consistent.

Fill to 1.0 bar cold and watch pressure as heating warms up and tell us!

You said pressure relief valve vent does not discharge. I think that it probably does. How did you check it?

Tony