Header tank backfilling - Not ball valve

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14 Sep 2015
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Hi Guys,

I'm having problems with my header tank at the moment and wanted your opinion on something.

The problem I've had is that for the last 3 months I've had the occasional leak from my header overflow. Nothing huge and when I run the hot tap for 5 minutes or so it went away and stayed away for a few days or more. I assumed it was a ball valve fault and left it. (Yes I know I shouldn't look for the quick fix but there's a lot to do at the house and this didn't appear to be that urgent).

So I finally decided to look into it properly and found that the ball valve is working properly, no leaks at all and yet when I isolated the valve and drained the header tank partially it was still filling up to the point way above where the ball valve would cut off which is why the overflow is leaking.

After reading a few posts I think I've found the problem. The hot water tank (Gledhill Sunspeed) has two feeds for showers and a third which goes to a mixer valve that I think is for hot water in taps. What I've found is that when I run a hot tap the pipe from the tank to the mixer valve heats up as you'd expect but then as soon as I stop the pipe instantly goes cold right back to the tank tapping. I'm thinking the pressure from the cold at the mixing valve is too high and that's what's causing the header tank to backfill.

I've tried altering the setting on the valve from "Max" but this results in the safety vent turning on in the header tank so is a no go.

My questions is : is it ok to put a check valve for the hot coming out of the tank and before the mixer to prevent the cold going back to the tank? Alternatively is this more likely a broken mixer valve?

Cheers,

Gareth
 

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Ok.

And from what I've seen online some people are putting check valves in before the mixer as a belt and braces approach. Is this a normal approach to it if replacing the valve? As you can see from the original picture there is only the pipes directly into the mixer from cold and hot.

Cheers.
 

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