High pressure in sealed system after turning heating on

[dona3853]

I was preparing to remove a downstairs radiator as it showed signs of having sludge last winter and was going to install a TRV and new lockshield at the same time. I needed to check which way the flow was as the radiator has 2 what look like identical valves. I therefore put the heating on for the first time for probably a couple of months. After a while I went to turn it off and noticed the pressure had gone through the roof - well just over 4 bar anyway. It had started at just a little under 1 bar and usually with the heating on it rises to around 1 and a half which I think is normal. After turning it off it gradually fell and after 2 days has now settled at around 2 bar. I am just wondering what may have caused this. I can't think that water is getting into the system bvia the filling loop as the high pressure only happened when putting the heating/ pump on. I have very little knowledge of heating systems so the inner workings of my boiler are a mystery = the way it should be for us novices. I do think it has some sort of expansion vessel in it so wondered if this was a symptom of that failing. Or if I do have sludge in the pipes could this cause a blockage that would increase pressure - although as far as I could tell water was flowing to and from all rads without a problem.

I was also concerned how high the pressure was going to get as I turned off the heating at over 4 bar and for all I know it was continuing to rise. I believe there is a pressure valve somewhere on the boiler but don't know where. Shouldn't it have kicked in before getting this high?

The boiler is an Ideal C95FF

Any thoughts would be appreciated.

 

[Reg Man]

Sounds like an expansion vessel problem. It has probably lost its charge. It may have a split diaphragm. You Could let the system cool down and release the water pressure down to 1 bar. Then check the expansion vessel pressure which should be charged up to about 1.4 bar. Word of caution. If this requires you to break into the boiler, you should not touch it, unless you are Gas Safe Registered.

 

[dona3853]

Thanks Reg Man. No I wouldn't dream of opening up the boiler. I'm going to drain down the system anyway and flush out that radiator. Then refill and see what happens. The boiler is due a service anyway so will get a pro in to have a look.

Would an expansion vessel problem also explain a gradual loss of pressure over time. For the last couple of years I have ocassionally had to open the valve to top up the pressure in the system as it gradually fell over a preiod of a few weeks. I had assumed we had a leak in the system somewhere but there has never been any evidence of a leak. Can sometimes feel a bit damp and see some water around a couple of the lockshield valves on a couple of the radiators but never enough for it to actuall drip. Nothing has ever come out of the pressure valve either.

 

[bigman]

The pressure loss was most likely down to the valves weeping, it doesn't take much water loss to decrease the pressure

 

[jtsplumbing]

You need to get someone in to check boiler ! if pressure is getting as high as 4bar and safety valve is not lifting you have a safety issue, as for TRV on your radiator most valves are bi-directional so does not matter what side it go's on