pressure too high

3 Dec 2007
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United Kingdom
when i bled my radiators at the weekend it seemed to empty the boiler. So i used the filling loop, but didn't turn it off soon enough. The system pressure gauge is between 2.5 and 3 bar when it's off, and 4 (maximum pressure reading possible) when it's on! I've bled a pint or so of water out of the radiators but it hasn't made a lot of difference. Should I just drain some more? I don't seem to have access to the pressure release valve, and can't see where it would discharge. Is the central heating return meant to be closed?

It's a gas boiler, Worcester Bosch 240 Combi RSF. Previously i was having problems with the thermostat cutting the pilot light after the (very) hot water was running for a while, I would use the overheat thermostat reset button to turn it back on.
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Is the central heating return meant to be closed?

No it should be open :eek:

Drain another couple of litres from a drain point on a rad, dont try using the PRV.
OK. It was on 2.6 last night when i went to bed, but in the morning it was 3.6. I drained a bunch more water at the radiators this morning and it came down to 2 bar. I was thinking maybe the filling loop was letting water in, so i turned the screw (on the loop, near the copper pipe) tighter ( i making a basic error here, should it be anti-clockwise to close???) and let some more water out. The gauge is now on 2.5. The screw further up the mains water-in copper pipe which the loop's attached to, is in the open position - should it not be?? (The central heating return is indeed open, it's just that in the manual diagram it's closed for some reason)

i hope i'm doing something stupid rather than have a damaged part - it seems likely, given that it had previously run dry....
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I should add that it isn't venting (much - a few drips) from the discharge pipe outside (does this mean the pressure relief valve could be stuck?). Bleeding the radiators isn't doing much there a drain point that would be more effective?

The red dial on the gauge is set at 1.4. I can't see a pressure valve in the boiler, and don't know how much air is in it. Where would this valve be? The filling loop screw head slot is aligned across the hose, as far clockwise as it will go. Could the filling control valve be the problem, and what would i be looking for if i disconnected the hose section?

thanks for the help
to be correct the fillup loop should not be left connected at all once the system is set at the correct ,because of water cross contamination from the drinking water to the heating system , so fill the system to 1 bar then turn off both taps the screwdriver slot should be across the valve on both valves, then disconnect the loop and use a cap on both ends of the valves just in case they leak and hang it somewhere it can be found
Ithe pressure valve is dripping outside it is going to need replaceing then all should be ok

My problem is i can't get it back down to 1 bar - it seems to go back up as fast as i get it down (haven't got it down below 2 bar yet) - presumably because there is water getting back in somewhere. There is no second screw on the loop, just the valve screw at the bottom of the braided hose....there is a nut in the equivalent position and the top, and there's a valve on the mains water in pipe. Is it the valve on the mains pipe you mean by the other tap?

I should add that the loop hose goes from the mains cold water in (lower end of loop) to the central heating return (upper end of loop), and the central heating return valve is open. I guess this is normal. Should I close the cold water in valve and then bleed the radiators?
OK...closing the mains cold water valve cut off the hot water taps, so that must stay open.

There's a drain cock at the bottom of the hall radiator - should i open that to drain the water quicker? Even if i do, though, it still seems to be coming back in...
FFS, close the isolating valves on the filling loop! Check the FAQs for details on this. Make sure that no water is entering through the filling loop by disconnecting it.
I've already said I have only one isolating valve on the filling loop and that I've closed it. I did know how to do this, but also checked the FAQs in detail before posting.
No. I guess I need a pipe wrench...and something to stop the water if it is still flowing?

Sorry if this is a bit of a 'hole in the bucket' routine 4U - if i knew what i was doing i wouldn't be here! :confused:
You can usually undo the flexi hose without a tool. The ends of the hose have projections to get a grip on with your fingers. If you don't disconnect the hose you won't know if you've turned off the water.
Think I've sorted it now - the loop was letting water in. I used the PRV inside the boiler to manually drain the boiler (much quicker and easier than using the radiators)...and then even i could hear the water coming straight back in. I fiddled with the screw-head slot on the valve until the water stopped. I currently have the pressure at 1 bar cold - the red dial is at 1.4, is this the minimum or maximum cold pressure required?

thanks for all your help.

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