Pressure Problem in sealed CH system

[bobknox]

I have a Potterton Profole 60E boiler with a sealed system (Bolier on ground floor)

Over bank holiday the boiler failed to start when CH cycle kicked in and the pressure of the system was just above zero. I was instructed by a family friend to bleed the rads while cold whcih I did and got air out. I then re pressurised back up (via filling loop) to 1 bar and then bled again and refilled until I was getting no more air from any rads - just water.

I started heating again and bolier fired up a remained lit but pressure rose up to just over 3bar. Water leaked from the overflow pipe and the pressure reduced some but still 2.5 bar.

I left running but later in day switched off heating and watched the pressure fall back down to say 0.5bar before I switched back on again (basically I didn't want the pressure to keep falling so that I couldn't put heat back on again).

Left running overnight and checking pressure thid morning the pressure has come down to 2bar and I'm assuming it will keep falling.

I have checked for leaks and weeping valves and can't find any and all rads heat up hot (even the ones I couldn't bleed due to painted over bleed valves).

Up until this system has been running without issue for 4-5 year since we moved in.

Other info. we have a 0.5bar expansion vessel fitted. Boiler is outside in utility room but with Frost stat fitted.

Any thing else I can check for?

 

[dal5band]

First of all I suggest you check the pressure whith the same conditions every time - e.g.cold. This will give a better idea on what's happening.

My mum's new combi had this problem and we discovered a small leak - a drip which dissapeared into the carpet. With this drip, the pressure went down by 1 bar in about a week and the boiler cut-off after about 2-3 weeks from full pressure (2bar). Plumber had to re-do a joint.

Keep looking for a very small leak.

 

[bab]

If you have set the pressure at 1 bar when cold then its lifting to 3 then discharging then down too 2 you hav e fault with ya expansion vessel. It may say .5 bar on it but it should have minimum 1 bar in it. can u see a valve can like on a car tyre.?