central heating pressure is going up when system is off

If your sure the filling loop valves are shut off completely (only real way to know is to disconnect the filling loop at the boiler end and watch for water leaking from it) , then the only other explanation would be holes in the heat exchanger, so water from the DHW (domestic hot water) side is leaking into the CH (central heating) side... (assuming this is a combi boiler)

 

As JJ says.

Almost certainly it's that the filling loop valves are allowing flow by, even tho' they seem to be offski. The loop should have two obvious valves fitted, one at each end. Work out which one is the cold rising main and which is the boiler system side. The former should have the akshull valve tap on it - a small plastic lever or summat. The other end will likely be a longer chrome valve and this is what's called 'non-return', so that system water cannot get back into the cold mains.

Unscrew the loop hose from either end, obviously leaving the valves in place...

Does the hose drip? Does the pressure stop rising? There's yer problem - a faulty valve. Easy to replace - just turn off the cold mains.

If, however, the pressure continues to rise with the hose disconnected, then you have a problem. Is it a combi or a system boiler? Either way, there's a perforation betwixt the system side and the mains. Nasty...

 

I'd agree with the above posts its 99.9% the filling loop, if its the sort with little plastic heads, the plastic somtimes breaks and even though they appear to be shut, they are not, take of the little plastic head and turn the spindle so the flat bit is across the pipe and not inline with the pipe,

 

Yep, it sounds unlikely, but akshully only one valve is a shut-off valve with an akshull tap; the other valve is a 'one-way' jobbie and is there to stop water wot has been put into the sealed system from getting out agin.

Chust disconnect one end of that hose. Question - does it drip? Ok, another question - does the pressure continue to go up with that hose disconnected?

 

the hose should be left disconnected anyway, get some 1/2 blank caps with some rubber washers and cap both sides.

 

http://www.screwfix.com/p/combi-str...rch-_-SearchRec-_-Area1&_requestid=313985#_=p

turn off water, open taps change the part on the mains water, leave the one on the 22mm pipe on,

 

If Your plate heat exchanger is ok just change filling loop by turning off cold main, drain htg from radiator or boiler, undo nuts on each end, fit new one with check valve on cold side, bobs ya uncle

 

That is the filling loop but integral in boiler, have you disconnected the 6mm copper tube between that valve & htg

 

I've never known both sides of that valve to let by. You need to cap the integral loop...caps should be provided, if not get some & cut a standard loop into pipe work, or contact supplier & check if under warranty 1st if not buy replacements & fit