Setting water and heater temperature on boiler and cylinder

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NorthnotNorth

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• 27 Dec 2019

• #1

My Vaillant ecotec plus 428 boiler lets me set both water temperature and heating temperature. My hot water cylinders also have a thermostat on them.

I want the hot water in the cylinders at 60C. I've currently got the thermostats on the cylinders at 60 and the water temperature on the boiler set to max at 65. Is this sensible, or should I turn the boiler down?

The heating is current set to the max - 75C. Am I right that turning this temperature down slightly could be more energy efficient?

 

CBW

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• 27 Dec 2019

• #2

From what I’ve been told by Vaillant technical, the heating thermostat should be around 62 degrees. Although the hot water one goes up and down, I don’t know if it has any bearing on a cylinder thermostat as it’s this one that’s governed by the boiler and zone valve.

 

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• 27 Dec 2019

• #3

The right hand knob on your boiler doesn't actually do anything. Its a commonrail design from the combination boiler.
Set your boiler flow to 70c and your cylinder thermostat should be on 60c. You can adjust the cylinder up a down 5 degrees to get it to a level that is comfortable. Cylinder thermostat are notoriously inaccurate as they are measuring the outside temprature of the copper tank not the water temp.
The only time your right hand knob would function is if the cylinder was a Vaillant one and you had bus cables and vaillant controller connected which is unlikely.

 

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• 27 Dec 2019

• #4

Thanks both! You're right - not a Vaillant cylinder. So is the idea to set the flow temperature to 70 now and then turn it down in summer?

 

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OvertonPlumber

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• 27 Dec 2019

• #5

No set at 70c on boiler and leave it there forever.
If you are demanding water at 60c you need a flow of at least 70c allowing for losses unlagged pipes etc.
You aim to store it at 60c distribute it at 50c and have it at 45c coming out the taps.

 

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• 31 Dec 2019

• #6

Thanks - that's really useful! I've got the water temp set to 60C mainly for hygiene purposes (to stop legionnaires etc). I think it's well over 45C out the taps - maybe because the pipes are well lagged - but I might get a mixer tap to resolve this...