CWCV in unvented hot water system - what is this?

Feb 13, 2015 3 Replies
E

Further to the thread 'hot water go slow' about our mains pressure hot water tank slowing to poor flow the bloke who serviced our boiler has sent me a note saying that the problem is "undoubtedly the CWCV".



This is not the pressure relief valve but I can't work out what this is



- presumably the V stands for valve but what is CWC? I believe it has springs inside.



He's given me the name of someone who can fix this who hopefully is around.



On this topic, I hadn't appreciated that these unvented hot water pressure systems are quite complex and potentially dangerous and advice seems to be that they need regular servicing or checking - is this correct?



E.


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A

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J

Sounds like the cold water control valve aka pressure limiting valve. See 3 on the diagram:

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They should be checked from time to time - the basic requirements being to check that the main safety valves operate (they have a red knob which can be turned by hand to test they open - the water discharge from each should be visible at the tundish - a small air break device), and to check the charge pressure in the expansion vessel. You would also want to check from time to time that there is no water dripping through the tundish during normal use since that would indicate either a failing valve or possibly a problem with the expansion vessel.

There are multiple safety devices built into these cylinders to ensure that they remain safe. (There was a former poster to this group who used to delight in posting a video of one exploding. However in order to get that to happen, you need to defeat multiple safety interlocks, and disable several thermostats in an electric heating system!)

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