Just installed a new DHW flow switch and microswitch on my Potterton Puma 100 as the diaphragm was passing water and had corroded the whole thing and shorted out the boiler. Install went OK and HW works fine now, but I notice that if I open and close a cold water tap quickly then it moves the diaphragm and cycles the microswitch and burner just for a split second. I can't imagine this is good for the boiler? I've checked the gap between flow switch and microswitch and is OK. Does this mean my DHW expansion vessel is faulty?
Potterton - cold water triggers DHW flow switch
- Thread starter ftgpmb
- Start date
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C
compheat
If you put a non return valve on the cold water inlet it should stop this happening, its a bit like water hammer that causes the flow switch to activate
H
holty
when you changed the diagphragm you would have isolated the cold, proberbly by means of mains stop tap.if so when you recharged the mains supply. youve proberbly got a deadleg somewhere.this could eventually disipitate with time.
and so it has hotly.... opened and ran all the hot taps for a while in turn to get the air out and now it doesn't happen. The bath (which is right next to the boiler) still moves the diaphragm when you really slam it off, but not enough to touch the switch, so all is good. I don't think I'll need a NRV after all.
Thanks for the help.
Tip for DIYers when changing the flow switch though, remember to get some washers before you attempt as the ones coming of the flow switch might not be serviceable.
Thanks for the help.
Tip for DIYers when changing the flow switch though, remember to get some washers before you attempt as the ones coming of the flow switch might not be serviceable.
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yes, was just thinking that a non-return valve wouldn't help. As far as I can tell, the pressure wave caused by shutting the tap is travelling up the cold water inlet through the boiler to the flow switch diaphragm. Neither a NRV on the inlet nor the outlet would help would it? Surely this is what the expansion vessel just above the CW inlet is supposed to take care of? That was why I was wondering if this was what need looking at.
T
thefloosyonthebeach
sounds like a 'dead leg'.
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