Scalding Hot Water - 3 port Mid pos Valve suspect?

MickOC · 5 Feb 2010

Hi,

HW is scalding hot (always has been), just wondering how to confirm 100% if Mid Pos Valve is faulty? I have tried turning cyl stat down to 50 and makes no difference, when I turn it up and down past the click I can here the valve opening and flow pipe to cyl gets hotter.

I have removed head and checked spindle can just about move with fingers, and can move easily with pliers - also moved head lever to manual when CH is off and can feel resistance so seems OK.

I've checked the flow pipe into to cylinder after CH has been off and cyl stat turned right down and it gets v hot, slightly cooler than CH side but not much. Is this normal due to heat transfer?

Do you think valve is suspect/passing?

seco services · 5 Feb 2010

if the flow pipe to cylinder gets hot with only ch on from cold it does sound like the valve is passing poss crud in the hw port or the paddle is worn/faulty.

MickOC · 5 Feb 2010

thanks, thought it didn't sound right, will replace then (£100!!)

MickOC · 5 Feb 2010

after thought - My HW has to be turned on at timer to fire boiler and turn on CH (timer missing HW off wire, so currently can't have CH on without HW).

So to test it, I turned cylinder stat to min then turned on CH&HW and checked flow pipe to Cylinder which was very hot - it should NOT be hot - correct?

seco services · 5 Feb 2010

so your only getting the hw port shut when the stat is satisfied.
you should get 230v on the grey wire from the valve when you turn the stat down.

if you ever turn your programmer hw off you will loose the power on the grey wire and the valve will not shut the hw port.

MickOC · 5 Feb 2010

Not sure I fully undestand what you mean. I know the programmer is not 100% correctly wired to Y PLAN block (missing HW off), I am due to fix that by installing a wirelss programmable room stat and just using the existing programmer for HW only.

I'm going to drain down tomorrow to flush out fernox restorer and add protector - and thought I could replace 3 way valve at same time if it's faulty.

So I guess I'm asking is what I did a good test and is it reasonable to assume it's at fault if cylinder stat was turned right down but flow to cylinder was hot? - but HW was switched on with CH while I tested it as that's the only way I can fire up boiler currently.

seco services · 5 Feb 2010

MickOC said:
Not sure I fully undestand what you mean. I know the programmer is not 100% correctly wired to Y PLAN block (missing HW off), I am due to fix that by installing a wirelss programmable room stat and just using the existing programmer for HW only.

you still need a hw off wire. unless you leave the hw on constant at programmer and let the cyl stat control it or you'll loose the live to the grey wire of the valve so the hw port will never shut.

So I guess I'm asking is what I did a good test and is it reasonable to assume it's at fault if cylinder stat was turned right down but flow to cylinder was hot? - but HW was switched on with CH while I tested it as that's the only way I can fire up boiler currently.

yes with hw on cyl stat turned down below cyl water temp then the cyl stat satisfied will put power on the grey and close the hw port.
but you must leave the programmer on constant and let the stat control the hw, if you turn the programmer off even with stat turned down their won't be power to the grey and the valve will never close the hw port.

MickOC · 5 Feb 2010

OK many thanks, so looks like the valve is sus and will need to be swapped.

I was going to run a new 3 core down the ducting for the HW off, but think the other option with new programmable stat and use existing 6400C for HW only is easiest (will move the CH ON wire on existing prgrammable to HW off- also means I get a room stat which we currently don't have.

seco services · 5 Feb 2010

sounds ok.

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Scalding Hot Water - 3 port Mid pos Valve suspect?

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