Hot Water Tank Thermostat

Discussion in 'Plumbers' Talk' started by SoulConspiracy, Aug 31, 2017.

  1. My hot water is way too hot and I finally got round to trying to sort it out.

    There is a thermostat on the side of the tank that's sitting inside a hole in the insulation. I've turned the thermostat down to 50 degrees but the water is still piping hot. I took the thermostat out and the surface of the tank is quite cool, I don't understand, why isn't it hot like the water is!? Anyway the thermostat can't be doing anything cause it's touching cold tank. There is another thermostat on top of the tank but I understand this is for the electric immersion heater.

    Anyone have any ideas whats going on?
  2. Wayners

    Wayners Active Member

    What are the pipes like coming out of tank when you run tap? One should get red hot
  3. Yeah, the pipe coming out of the top is red hot. I've put the thermostat against that hot pipe to see if I can stop the water heating up too much (that's probably a mistake).
  4. Wayners

    Wayners Active Member

    The immersion is heating water? Do you have a boiler?
  5. The immersion is turned off. I have an oil boiler outside, it's not a combi boiler.

    Could it be that I'm not touching the bottom half of the tank when it's hot, I'm only checking it after we've had showers. Maybe the thermostat is broken?
  6. DIYDave.

    DIYDave. Well-Known Member

    Difference in temperature of hot water at taps compared to surface of cylinder, assuming your touching the copper tank (or s steel) indicates a scalled up tank. Scale acts partially as an insulator on the inside of the tank walls, hence outside of tank feels cooler, long term, not so good though
  7. DIYDave.

    DIYDave. Well-Known Member

    Sounds like op is talking about tank stat not immersion heater / stat
  8. That sounds bad, like the tank would need replacing. :(

    I think I am talking about the tank stat. There is a different stat on top of the tank (connected to a plug that has "immersion" written on it).
  9. Devil's Advocate

    Devil's Advocate Well-Known Member

    What does 'red', 'scalding' and 'piping' hot mean? Water temps mean different things to different peeps.

    Anyhoo, assuming that the water coming out the top is genuinely 'too hot', then you can test the cylinder thermostat by simply turning it up and down.

    You say the tank side under the 'stat feels cool, well if you note where the 'stat 'clicks' you should have a good idea of its actual temp; rotate it slowly up and down around the click point, and note the rough middle position of each swing. See what that says.

    Also check that the motorised valve operates every time you 'click' the 'stat.
  10. The tank does get hot, I was just feeling it at the wrong time I guess. Doh!

    The water is definately too hot. I have a thermometer at home, I'll see how hot it really is. The thermostat is turned right down (50 degrees) but the water is too hot to touch for more than a split second without scalding.

    I guess I have to catch the water when it's within the thermostats range if I want to test the thermostat clicking on and off.

    If the motorised valve is bust the I guess I'll get a click from the thermostat but no noise from anywhere else?

    The metal contact from the thermostat isn't actually touching the tank, it seems to be designed that way, is that a problem. Looks like a drayton HTS3 type (but maybe a bit older than what you can buy from a shop today.
  11. Thanks for your help. I feel like I'm learning (mild headache).
  12. Devil's Advocate

    Devil's Advocate Well-Known Member

    If the water is even 'warm', the 'stat should be clicking - it looks as tho' it goes right down to around 40oC.

    If the cylinder is hot at its top, then the stat should definitely be within range - are you saying you can't hear any clicks at all?

    What sort of diverter valve do you have - does it have 3 ports (pipe connections)?
  13. Will check all this stuff out when I get home.
  14. 3 port valve.

    Water is 65 degrees, I measured tge temperature.

    Cant hear anything clicking when ibturn the thermostat, does this mean its broken?
  15. I think the problem was the thermostat not touching the tank. Stupidly designed device. I've stuffed the gap with tinfoil. It seems to be not heating when I switch it to constant.
  16. Yes, I feel this has solved the issue.
  17. MGW

    MGW Active Member

    60˚C is normally considered as the lower limit due to legionnaires disease, you can get mixers that go on the tapes to reduce it further, seems you have cured the problem.
  18. nigel willson

    nigel willson Well-Known Member

    Normal way to fix is not foil. Cut out a bit more insulation to put the stat against the cylinder.
  19. Its the metal sensor set back into the housing of the device, bigger hole in insulation wont help. Its the kind of job you'd need a bodge to sort out, cant think of any way better than the tin foil.
  20. nigel willson

    nigel willson Well-Known Member

    Deeper not bigger, so that it touches the cylinder.

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