Boiler too much pressure !

[bc123456bc]

Since we moved into our new house 6 month ago we have had a problem with the boiler loosing pressure. It had to be topped up every couple of weeks. The pressure would drop off to under .5 bar and we would top it up to 2 bar and immediatly would drop down to 1 bar and run at that for a couple of weeks until the next top up.
With the recent hot weather the heating wasn't used for 2 weeks and when it was used after this break the pressure gauge began rising and was up to 4 bar within 10 mins!! I thought the release valve should blow off at about 3 bar but there is nothing coming out the overflow pipe. The heating is now off until its sorted. Any ideas ??
Thanks.
Bob

 

[ajs heating]

release some pressure from a radiator bleed valve.

as for the prv should activate at 3 bar, but i have come across ones that have jammed.

as for pressure rising when heating on maybe be your expansion vessel needs charging or split. it will useally fall again when heating off.

check your filling loop is fully closed and not passing water.

drain some from your rads till it is about 1.5 bar then switch heating on see if it gos up then turn heating off see if it falls again.

 

[fuzzy]

top up to 2 bar is too much, top up to 1bar.

probably the exxpansion vessel, have you added any rads to the house? how many rads by the way ?

 

[bc123456bc]

there is 6 radiators in the house in total, today i opened the bleed screw in 1 radiator untill pressure read 0. then I presureised the expansion vessel to 22 psi closed off the bleed screw and topped up water to 1 bar. turned on the heating and within 5 mins it was up to 4 bar again !!! will have to bite the bullet i think and call out an expensive engineer !!!!

 

[Paultheplumber]

Have you checked the recomended pressure on the expansion vessel it should say if it is under charged it wont make much difference also is there water coming out of the valve if so the diaphram is split and the vessel needs changing.

 

[bc123456bc]

I pressed the valve to let a little air out the expansion vessel and no sign of any water in it. Looked through all paperwork for boiler and it doesnt list a recommended pressure.