Worcester heat slave pressure problem

8 Mar 2005
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United Kingdom
I run a Worcester Heatslave sealed system. I returned recently to find system pressure 0. I top it up to the required 1 bar and fire it up. The pressure climbs up until it reaches 2.5 bar which I think is a little high. So I bleed it off until 1 bar is achieved. When the system is switched off overnight pressure drops to 0.....Thinx - since there are no leaks - is it possible that the expansion tank pipe could be blocked or are greater dark forces at work?
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The expansion vessel needs attention, search the forum, loads of info.
The heat slave has one of two types of expansion vess a square one and a round one if its the square the flexi hose feeding it has a habit of blocking up giving the symptoms of a faulty expansion vess (your symptoms) to check if its the hose raise the system pressure to 1.5 bar then test the pressure at the air valve on the vess using a tyre gauge and record the result ,remove the system pressure from the boiler down to zero then testy again if you get the same result then the flexi is blocked and needs replacing .if you do replace the hose remove the burner out of the way and cover as the pressure of water trapped in the e/vess will go all over.
Many, many Thanks to both Oilman and Cog,

Cog- I tried what you suggested and there was no change in air pressure! I had a slight suspicion since the connecting hose never seemed to be hot indicating that nothing had flowed. I've always enjoyed taking down hose - life is so exciting.
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remove the copper pipe from teh expansion vessel and stick your little finder in the vessel (nothing else) and the rubber diaphragm should be pressurised and taught, if you cannot feel the diaphragm then it has perished, remove the valve cap, it looks like a car valve and connect a foot pump, pump up the valve and if the diaphragm is fauty you will hear air coming out at the other end, The air pressure is meant to be 10psi. good luck
...............The air pressure is meant to be 10psi. good luck

The air pressure is meant to be equal to the static pressure of the system, though some boilers (particularly gas) are fitted with pressure switches which may require a higher pressure.

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