Pressure rising when heating turned on

[Sharon Willis]

I have gas heating, and today we had to take a radiator off to do some decorating. Took it off, then put it back on later, but obviously the water had come out. So we re-attached it, and tightened everything up (my dad's plumber friend gave us instructions, so I think we did this basically ok). Opened the thing that you use to bleed it.

The system pressure was really low by now, so i re-filled it to bring it up to normal. Once we had checked that nothing was leaking, we turned the heating on again. All seemed OK, except that the radiator we had removed didn't get hot (the others did). We closed the thing where you bleed it. I noticed that the pressure was going up - usually it's at about 1, but it gradually (over half an hour or so) went up to just over 2 (max on the gauge is 4). We turned on a hot tap, and it jumped up a bit more, and went back down when that was turned off). Once we turned the heating off, the pressure gradually fell again.

I've never noticed it go up before when the heating was on, but maybe i've just never looked. There's also the fact that the radiator didn't warm up.

Any advice?

 

[gasmanrob]

Pressure increase is usual when heat is being produced as water is heating it's volume is expanding then as it cools it's volume settles back again.

as for your rad not coming on is one of the valves a thermostatic radiator valve as it is possible the pin has stuck down following you shutting it off

 

[IDCHAPPY]

Sounds like your expansion vessel in your boiler needs checked or replaced, the water is expanding during the heating cycle so if there is a lack of expansion then the pressure increases 🙂.
Needs Checked I'm afraid.

 

[Sharon Willis]

Sounds like your expansion vessel in your boiler needs checked or replaced, the water is expanding during the heating cycle so if there is a lack of expansion then the pressure increases 🙂.
Needs Checked I'm afraid.

Thanks. It was fine this morning - could it have broken as a result of what we did? The boiler was serviced a month or so ago.

Could this be dangerous, or would it cut out if the pressure got too high? And is it ok to have the hot water on until we get this fixed -keeping the heat off is not a problem, but we need hot water.

It is a radiator with a thermostat... The pipe leading to the radiator gets hot, but the radiator itself doesn't.

 

[Simon F]

the expansion vessel is probably in need of checking, but doesn't sound too worrying.
the rad not working, as said trv pin, or possibly an air lock has been created because of the work.
check rad valves first, if no joy then progress to closing other valves to force air lock out.
maybe best to get your dads plumber friend to take a look.

 

[Sharon Willis]

Bleeding has reduced the pressure; it's still rising slowly when the heating is on, but seems to reach a maximum of about 1.5 (from being 1 when all switched off). Then it goes down again once the heating is switched off. It also goes up by about 0.25 when we turn on a hot tap, and then straight back down once we turn it off.

Took the thermostat off, and loosened the little pin thing, and now the radiator is warming up.

A couple of people have said that the pressure should rise slightly when the heating is on, and not to worry about that... Is that correct? If so, I think that's probably all that's happening.

 

[Dotty]

Is that all it's rising by?

It's fine. water expands when heated and a rise of 0.5 bar is to be expected, same for when you use the hot.

You may also need to rebalance your system.

View attachment How To Balance Radiators.txt

 

[Sharon Willis]

Is that all it's rising by?

It's fine. water expands when heated and a rise of 0.5 bar is to be expected, same for when you use the hot.

You may also need to rebalance your system.

View attachment 18337

Yes. It was more earlier, but now it's just going up by a little bit. So I think it's ok.

Thanks everyone for the help!

 

[WaterTight]

why was the pressure guage showing a rise in pressure when she used a hot tap?

 

[Leemckie91]

If its loosing pressure when it rises chances are the expansion vessel needs re charging or replacing, get a heating engineer to check it out.

 

[Simon F]

why was the pressure guage showing a rise in pressure when she used a hot tap?

an instant rise in pressure on the dial when the system fires up is probably due to the pump proximity to the dial,
rather than the whole system actually increasing in pressure.