Thermistatic mixing valve running cold?

14 Feb 2003
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United Kingdom

I have just fitted a thermostatic mixing valve to the water system on my yacht, this is the first time I have used one.
It is not working however, when you open the hot water tap warm water comes out for around a second, then it goes cold and stays cold.
Closing the tap and waiting a while, has the same result - warm, then cold.
The water in the tank is hot.
The TMV seems to be set to max temp, Adjusting the head (turning anti-clockwise) any further results in water coming from the valve head, I don't know if this is normal, adjusting CW stops the water leak.

Can anyone advise if it is either, too much imbalance on the water pressure (i.e. too much pressure on the cold side) or a possible faulty TMV?

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What pressure is your cold water supply to the valve?

I'm afriad I dont know, it's run by a water pump that shuts off when an internal pressure is reached. I estimate it's around 1.5 - 2 bar.

The cold feed goes straight into the tank bottom (with a branch off for the TMV) and hot draw from the top - the same as a house hot water cylinder but much smaller.

The cold pressure and the hot pressure is only (thoretically) different by the weight of the water in the hot water tank which is 5 gallons with a heigt difference of 30cm (approx) between the cold inlet and the hot draw outlet.



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