Hot Water Temperature

Hi All,
Possibly a rather dappy question but should I adjust the temperature of my hot water using the dial on the boiler itself (graded at 'cold', 'warm', 'warm/hot', 'hot') or a dial I've noticed on the hot water tank which looks to be graded in degrees C.
Just moved into a new house and therefore have a new heating system to learn the intricacies of. The (gas) boiler and hot and cold water tanks are all up in the loft. I'm getting some spluttering problems from the hot water, and I did see a sugestion in another thread that turning down the hot water temp may help...
TIA
Alastair
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The one on your boiler affects the temperature of the water in the circulating water that heats the radiators and the cylinder. This will cause the radiators to change temperature. Low is efficient thermodynamically and safer for kids. High causes more heat output.
The thermostat on the hot water cylinder determines the temperature of your hot water. This should be set to around 55C.
However, your circulating water MUST be AT LEAST 5C more than your hot water temperature. Otherwise, the hot water cylinder will never heat up enough to trip the stat, which will be very inefficient, as the boiler will never turn off properly.
The boiler temperature should be set to just less than max, unless you can spare time to experiment scientifically to ensure adequete radiator and hot water performance, or your entire system has and is optimised for a condensing boiler.
Christian.
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Thanks for the tips. That all seems to make sense. I'll try turning the water tank thermostat down a bit and see whether the hot water gets a bit cooler. We don't have any children but that doesn't mean that the hot water couldn't still scald someone. I think also I'll spend a bit of time studying the layout of pipes and wires to try and get clear in my head how the system works.
I've lurked here for years but never needed to ask any questions. I'll probably be back soon asking something else. :o)
Cheers Alastair
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Watch out though. If you have a standard size tank (900x450), you aren't actually storing much water. By dropping the temperature, you may find you run out of hot water in use, as you are storing less energy. If this happens, you should fit a thermostatic mixing valve to the output, where you can set the output temperature directly, whilst still storing the hot water at 60C or so, which gives more stored energy and better resistance to bacterial infection. It will also prevent boiling water being issued from the taps in the event of an immersion or boiler thermostat failure.
Christian.
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Valid point, I'll bear it in mind. Guess it could be a tightrope balancing act-type thing : turn down too far - run out of water; have it too hot - get scalded at some point. Thanks again.
Alastair
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Does your tank have an electric immersion heater in it? Tanks on their own cannot of course actively heat water. Presumably your water is normally heated from the boiler, so that is my guess as to where to adjust the temperature. Check and see if you have an electric immersion heater in your boiler and whether it is normally off. A lot of boilers simply try and achieve a temperature change ( delta T ), and so the temperature of the incoming water affects the temperature at the taps, so systems lke that need seasonal adjustment.
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