Water not fully heating up...

Discussion in 'Plumbers' Talk' started by Not Too Sure, Apr 14, 2021.

  1. Not Too Sure

    Not Too Sure Member

    Hi, quick question - if I switch my hot water on and the boiler fires up ok, if after a while the boiler turns off but the water is still only lukewarm, does that point to a thermostat related issue in the hot water cylinder?

    Central heating works fine and the HW zone valve seems to be working correctly - just seems that the water isn’t getting completely up to temp.

    I have an unvented megaflow cl250 cylinder.

    thanks
     
  2. BiancoTheGiraffe

    BiancoTheGiraffe Screwfix Select

    Thermostat would be the first thing to look at, and the cheapest part to replace...

    How old is it?

    If there's nothing wrong with the stat, the thermal cut out could be faulty and kicking in too early.

    How are you with electrics? Got a multimeter?

    Both of those can be tested easily with the right kit
     
  3. Not Too Sure

    Not Too Sure Member

    Thanks it’s about 12 years old

    I don’t think even the electrical immersion switch is getting the water up to temperature now either...so sounds like it could be the thermostat?

    Thing is I think there is an upper and lower thermostat on the cylinder - how would I know which one is the issue?
     
  4. BiancoTheGiraffe

    BiancoTheGiraffe Screwfix Select

    Quite possibly.

    I'm not a pro plumber so there may be something far more complicated that I'm not aware of, but I'd definitely start with the stat

    I had to replace mine a few months back as the plastic dial mechanism and gone brittle and fallen apart. The arrow on the knob was pointing at 70 degrees, but inside the mechanism was on 40
     
  5. Not Too Sure

    Not Too Sure Member

    Only thing is I think there is an upper and lower thermostat on the cylinder - how would I know which one is the issue?
     
  6. BiancoTheGiraffe

    BiancoTheGiraffe Screwfix Select

    The lower one. The upper element on a tank is usually for a short term boost only
     
    Not Too Sure likes this.
  7. Not Too Sure

    Not Too Sure Member

    brill - thanks
     
  8. nigel willson

    nigel willson Screwfix Select

    Different thermostat is used for the immersion heaters against the one for the boiler side of things
     
  9. nigel willson

    nigel willson Screwfix Select

    Different thermostat is used for the immersion heaters against the one for the boiler side of things
    they are elements not thermostats
     
  10. The Happy Builder

    The Happy Builder Screwfix Select

    Do not try and do any DIY repairs to the cylinder and its thermostats.

    You need a skilled and qualified person to check them out.
     
  11. Not Too Sure

    Not Too Sure Member

    Just as an update - I changed changed the bottom thermostat and all sorted
     
    BiancoTheGiraffe likes this.

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