Hot water at taps is too hot

14 Jan 2007
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United Kingdom
Hi all,

I've been trying to get the hot water temperature in my new flat (bought) under control as it's been scalding hot since we moved in.

My initial theory is that the cylinder thermostat was broken, so I've replaced that twice now and it still seems far too hot when set at just 60 on the thermostat valve - very painful to touch, like from kettle.

The tank is fed from a Gas boiler with a fully pumped system. The actuator and pump are working fine. It's a British Gas branded system, which is a re-badged Drayton system. The thermostat is a Drayton HTS3 (original was labelled BG CS1).

The thermostat is seated 1/3 up the tank and the area of insulation has been well cut away to expose the copper. The area it sits on is very hot to the touch when the heating has been on for 40+ minutes. Yet it only seems to 'click' off when I turn the control down to about 50...

The HW only comes on for 30mins in the morning and a top-up of 20mins in the evening. The Gas boiler thermostat is turned down to just '1' on the dial.

I can't believe I've had 2 duff thermostats in a row - is there something I'm missing, what else could cause the hot water to get that hot?

I live in London - could the tank be scaled and insulating the water from the thermostat? Does that happen?

I think I need to get a thermometer too and test the temperature more objectively...

Anyway any tips on why I keep getting very hot water from the taps would be much appreciated.

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Put your heating on and check the pipe from the three port going to the cylinder coil, is this as hot as the pipe going to your heating ?
It may sound obvious but check there isnt an electrical immersion heater in the cylinder that has been left switched on
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Hi folks,

Many thanks for the tips, here's my findings:

gigz: I've just tested that now and the pipe going to the tank coil is as hot as the pipe going to the heaters. I think this might just be because the water in the tank is very hot at it's heating the pipe to the 3-way. I have previously tested keeping the hot water off on the programmer but leaving the heating on and the hot water tank does go cold so I concluded that the 3-way and actuator seem to be working ok. I think I'll test again (don't like that the pipe to the coil got hot just now!)

Update: Ok, I've just touched the pipes again after having the heating on for 15mins and the pipe to the coil was still hot, and then I touched the other side and almost burned myself! :p D'oh! No lasting injury, and it has convinced me that the actuator and 3-way are working fine now!

ianmcd: Nice thought, but there is no electric immersion coil in the tank. That might've explained it though, so thanks for the suggestion.

xr4x4: Not being funny at all! I replaced the thermostats like-for-like with the wiring, so it could be that the original one was wired badly and I've wired up the following two - also badly! However, I think it's probably ok as when I turn the dial to the test position, it does switch the 3way off and on. With the old one I also pressed the metal that detects the heat to manually make it 'click' and it switched the heating on-and-off as expected. I think I'll double check this two as I'm starting to worry I was a little quick with my last rewiring I did!

I'm going to buy a thermometer today so I'll be able to be a bit more accurate with my 'it's very hot' measurements!

Thanks again for the help so far - anyone else know why a system like mine that seems ok would be heating the water so high?
Two things.

Buy a thermometer and see what the actual temperature at the tap is

Leave the HW set to off at the programmer, and the CH set to on, see if the cylinder still gets hot and both legs at the three port valveare still hot.

How long has it been like this?
Hi folks,

I have a confession to make...

So I did buy a thermometer and learned a very important lesson - my hand is a *TERRIBLE* judge of temperature and I should have much more faith in thermostats.

I put on the hot water for an hour and then held the thermometer under the tap for several minutes and the mercury only got to about 56degrees with the tank thermostat set to about 60 (guess that makes sense that the 4 or so degrees gets lost in the pipe work).

I think previous flats I'd lived in probably had hot water too low and I'd got used to that and thought it was 'normal'.

JohnD: thanks you were right on the money - I needed a thermometer and stop using my hand for judgement. Anyone else who thinks there water is too hot - get a thermometer and check first!!

Cheers folks,
A slightly embarrassed Chris :oops:
Due to my asbestos hands I have to have the cylinder stat at 65c as 60c just isn't hot enough to wash up with.
Due to my asbestos hands I have to have the cylinder stat at 65c as 60c just isn't hot enough to wash up with.

Im an absolute woose I couldnt keep my hands under 50c never mind 65c

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