Boiler pressure rising when turned on!

Silkwood

Hi guys,
Having an problem with my boiler at the minute. When its turned on the pressure gradually (over a period of about 30 mins) rises by about 1.5 bar. When turned off the pressure slowly drops again. I've set the cold pressure to about .3 bar so at the minute so it stays below 2 bar when hot. Any ideas what is causing this? Its a closed system btw.

Billy Bunting

Raise the presure to 1 bar, vent all rads and recheck and set to 1 bar, test.

shane0007

Silkwood wrote: »

Hi guys,
Having an problem with my boiler at the minute. When its turned on the pressure gradually (over a period of about 30 mins) rises by about 1.5 bar. When turned off the pressure slowly drops again. I've set the cold pressure to about .3 bar so at the minute so it stays below 2 bar when hot. Any ideas what is causing this? Its a closed system btw.

Your expansion vessel is probably split. Test at the pressure test point to see if water comes out. If just air, it may need re-pressurising but you will need to drain water away from the vessel to test.

Silkwood

I've already vented all the rads, didn't help.

Silkwood

Hi Shane, there was no air in the expansion vessel.. I just got a very slow drop of water coming out.

shane0007

The diaphragm in the vessel is split. You will need to replace it. Do not use the heating until this is done as further problems will arise and therefore more cost.
Replacing the vessel is very simple. Is it gas or oil and is the vessel an integral part of the boiler or is it located externally of the boiler?

Silkwood

It's a gas boiler. The vessel itself is on the heating pipe into the cylinder, well away from the boiler.

shane0007

Then it is a job you could do yourself if you feel capable. Drain enough of the system zero pressure & to below the level of the vessel. Unscrew the vessel, use ptfe or hemp & uni-white on the thread of the vessel. Ensure pressure of new vessel is 1.0 bar. Screw on new vessel and refill system to between 1.0 and 1.5 bar pressure. Bleed system, especially the auto air vent at the coil of the cylinder.

Silkwood

Thanks Shane.