Boiler pressure gone up???

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22 Feb 2008
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Hi

After recently finding my PRV was leaking I took it off to replace but ended up just cleaning it out as all the plumbers merchants were closed when I took it off on a Saturday at 11.30am.

This clean actually stopped it leaking and I thought i would give it a few days just to check before I put in the X100.

So to put in the inhibitor i tried to isolate the bathroom rad and syphon out a litre of water, unfortunately the little bit of pipe I had in the house wasn't long enough so I drained water from the upstairs rads from the bleed valves to drop the pressure in the hope that once the pressure had gone the water would follow gravity and flow out of the rad in the bathroom (the highest rad in the house). Using the bleed valve took ages so I just went to the drain valve downstairs and took out water till the pressure on the boiler was at 0.

I chucked the x100 in the bathroom rad. Filled up the system from the mains to 1.6 bar, bled the rads until all air was out and the system was at the recommended 1.3 bar. (boiler cold)

The bit I can't understand now is that last night when going to bed (after the heating had been on) and the boiler had been off long enough to reduce the pressure it was on 2.5 bar and the PRV had released some water outside.

I went around the house again bleeding the rads, but no air came out, only water. I did this until the pressure went down to 1.5 bar and waited till this morning to see what's happening - This morning pressure whilst hot was 2.1 bar and then went back to 1.5bar when cold. I've now taken out a little more water to reduce the pressure to 1.3bar but how could the pressure have gone from 1.3bar to 2.5bar?
 
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Firstly ensure the filling loop is closed properly.

The expansion vessel may need pumping becuse it has lost some air.
 
The pressure would rise if there is not enough air for the water to expand.
 
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If the expansion vessel has lost it's charge pressure you will see a higher than usual rise in pressure when the system heats up.

Mike
 
system seems to be behaving now - going up to 2 bar when heating is on and returning to 1.3-1.5 bar when off.

Nothing is coming out of the PRV pipe so I'm gonna watch the system to see what happens.
 
system seems to be behaving now - going up to 2 bar when heating is on and returning to 1.3-1.5 bar when off.

Nothing is coming out of the PRV pipe so I'm gonna watch the system to see what happens.

Just in time for Christmas :D

Merry christmas
 

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