Boiler heating water too hot (but boiler thermostat set at 60c)

Discussion in 'Plumbers' Talk' started by SomeOfTheGear, Aug 21, 2021.

  1. SomeOfTheGear

    SomeOfTheGear Member

    Our domestic hot water is coming out really hot, too hot to touch. Overall the timings of the heating and hotwater are controlled by a Tado unit which is working fine. There's a Rhino oil boiler that feeds into ACV Smart cylinder and there's an immersion fitted into the cylinder. The immersion heater is definitely off at the wall connection and also at a separate isolator switch in the kitchen, so I don't think this is the problem.

    Inside the boiler cabinet, there's a temperature switch with settings from 90 to 60 and it's set to 60, I've adjusted the knob (it'll only go anti-clockwise towards the 90 position) with no success. I also tried checking the position of the knob and it's fitted properly on the spindle so it's not twisted around out of position. My guess is that there's possibly a fault on the thermostat. What do you think?

    Where do I go from here?


    Last edited: Aug 21, 2021
  2. andy48

    andy48 Screwfix Select

    1. I'd suspect either the thermostat in the cylinder or the motorised valve controlled by that thermostat.
    2. Its an unvented hot water cylinder, which means that only a G3 qualified engineer can work on it. Its not DIY.
    3. Unvented cylinders require an annual service by a G3 qualified person.
    SomeOfTheGear likes this.
  3. heatyman

    heatyman Well-Known Member

    Presumably your cylinder is fed through a Y plan or similar. It is the thermostat on the cylinder that controls your water temperature, but bear in mind that the thermostat measures at approx 2/3rds down from the top of the cylinder where the take off is. When that thermostat measures 60o C, the water above it is likely to be significantly higher, especially if hot water usage is low.
    If you have children or vulnerable adults with access to hot taps, then consider thermostatic mixing valves.
    SomeOfTheGear likes this.
  4. SomeOfTheGear

    SomeOfTheGear Member

    Thanks for the replies guys, now that I know it's out of my league, I'll give our plumber a call. Best get baking, he likes cake!
  5. Mike83

    Mike83 Screwfix Select

    If boiler thermostat is set at 60 then the hot water shouldn’t get hotter than 60 regardless what the cylinder stat is set at.
    If it does it indicates the boiler thermostat is faulty.
    But if you have a blending valve it could be that.
    SomeOfTheGear likes this.
  6. woodbutcherbower

    woodbutcherbower Screwfix Select

    What a star. If only all customers were as kind and considerate as you.
  7. Jimbo

    Jimbo Screwfix Select

    Incidentally 60°C is far too hot to touch. There is no need for any tap to be more than 48°C and as said thermostatic mixing valves at point of use are the answer. Being oil you want the boiler flow temperature as low as possible (assuming it's a condensing boiler) that will still heat your house properly.
  8. nigel willson

    nigel willson Screwfix Select

    Stratification! Top gets hotter as stat lower down
    SomeOfTheGear likes this.
  9. Mike83

    Mike83 Screwfix Select

    That’s perfectly logical if the boiler thermostat is higher than 60.
    But if the boiler thermostat is at 60 then the flow pipe at the cylinder shouldn’t get hotter than 60.
  10. heatyman

    heatyman Well-Known Member

    Thermostat setting on oil boilers is very subjective. This is why many oil boilers only have a thermostat that indicates high and low. The location of the phial in the pocket is also very hit and miss as many no longer have any tension springs or even any conductive paste.
    SomeOfTheGear likes this.
  11. SomeOfTheGear

    SomeOfTheGear Member

    I can't understand people who aren't courteous to people working in their homes. I've also found that you get a lot further with sweet than sour!

    We had a guy install a new Wood Burner recently, he was here over 3 days, lovely job. My partner kept him brimfull with coffee and cake and sent him home a batch of Fairy cakes when she heard he had 2 little kids. 3 days later, a bird found its way into the new chimney whilst I was away. She called him up to ask for advice, he said I'm passing this afternoon, I'll pop in. He released the bird and showed her how to do it next time and wouldn't take any payment. I called him up the next day and said, thanks for coming, how much do we owe you? Nothing he said, I insisted so he then said your bill was several slices of cake and 8 fairy cakes and it's been paid in full.

    Will we use him again? Of course. Will he want to work for us again? I hope so.

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