Lazy hot water thermostat?

sagesse

I wonder if anyone has any suggestions? My hot water tank is in the attic. It has a conventional contact-type thermostat (Honeywell or somesuch) strapped to the outside, with its face in contact with the copper of the tank, and the insulation cut away around it to allow this. The problem is that it works ok in winter, when the ambient temperature of the attic is cold, but on hot summer days, we get no hot water. The attic gets to about 30 degs in the sun. Are these types of thermostat simply not up to it, does the bi-metallic strip get 'lazy', or is there a better type of thermostat available? A possible solution would be one that could be hung in the tank (it's an Elson with a removable lid).
Thanks (in desperation)

tonyh66

thermostat should be set to around 60C

MoneyMate

On what you have mentioned I would fit new Thermostat
http://www.toolstation.com/shop/Salus+Cylinder+/+Pipe+Thermostat/p50441
Also if you live in a Hard water area it may be the inside of your Hot water tank may be Scaled up, if so this can cause poor reaction to temperature changes, as scale can act as an insulator.

sagesse

Thanks, is set to about 70. Tank is at least 30 years old...I'll check for scale build up...there is a bit of sludge in the bottom, though thermo is about one third the way up, and as Honeywell suggest, I'll fit a curtain wire round the tank to ensure max contact pressure. My best bet is that it's just not functioning as well as when it was new. It probably works on a bi-metallic strip, so I'd be interested to know if these suffer 'fatigue', before I go off and replace it. It'll be the third one in 28 years but I dont know why I cant expect infinite life.

MoneyMate

I think you can get a compound ? To fit around thermostat to help with conductivity , Worth checking out.

Ainsley1

It does sound as if there is something wrong with the stat functionality but you can check it out.

Make sure there is good contact between tank and stat, close fitting no insulation/dirt causing a gap and a spring wire to maintain contact. All aid to stat measuring water cylinder temp rather than ambient temp. Conductive paste is usually not necessary but will help. Small tubes available from electronics suppliers (probably Maplin just as one suggestion) or plumbers merchants but maybe in too large a quantity from the latter!

When all that is checked/done try, with the water hot (near 60degrees C if possible) to change the 'trip' temperature on the adjusting screw of the stat. Best if you know the water temp but otherwise the lower temp of hand hot estimate will do. (if you have a boiler system then if you cannot override you may have to use your immersion heater to get the cylinder contents up to temp!). The bimetallic strip should change over (you should hear a click) as you increase the desired temp passed the actual water temp and click again as you reduce. There will be a small difference between increasing (desired temp) and decreasing when you hear the clicks. [This is normal due to an effect called hysteresis and is advantageous to stop the heating constantly switching rapidly on and off by requiring a significant fall in water temp before switching on.] This should be in the range of 2 to 5 degrees so make sure that is roughly what you get.

If the test fails replace the stat. Set at 60degrees not 70 as that higher temp can cause burns to skin straight out of the tap and 60 is too hot to stand anyway 38 being more comfortable hand hot. 60 however will reduce any bacteria build up but 30+ish is a breeding ground!

Insulation outside the cylinder and stat helps to reduce fairly small effect of the ambient temperature on stat working that might occur with a large swing in air temperature (say from 30 degrees down to past freezing point).

Hope that helps you.

p.s. if water still does not get hot enough you might have a heater problem rather than a stat issue.

sagesse

Gentlemen, many thanks, plenty here to be getting on with!