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What temp should i be setting my boiler to ??


Prominent Member
I've just in the past 2 months had a smart meter installed which is giving constant readings.
This has pushed my dual fuel bill up from £88pm to £118pm.
Looking to try and reduce the electric and gas bills.

at the moment the ancient programable timer next to the boiler has been turned off and we rely on the thermostat at the top of the stairs to control the heating.
I know this can mean that the house is heated with nobody in but in all honesty due to my shifts there would only be nobody in the house for most of the day about one week every 4 weeks.
The temp on the thermostat is set for 21 (GF sometimes finds this cold).

I've got a Valiant Eco Tech (Housing Agency Property).
There are two dials. One has a tap symbol & one has a rad dial.
What temp should i be setting the tap (should it be just below scalding temp) and what setting should the rads one be set too ??

The house is a 2 bedroom 1930's terraced house (4 connecting houses that the 2nd and 3rd house are separated by a alley but joined at the upper wall)

Jean Valjean


Distinguished Member
For the hot water I would imagine that hot enough for whatever function requires the hottest water. ( I like washing up water way hotter than I like my shower water, for example). Or you could say the hot water is at the right temperature for the bulk of jobs and other functions like washing up can always be boosted with a boiling kettle etc.
As for the radiators, the hotter the water, the quicker the place will warm up but more heat will be lost between the boiler and the radiator. A lower temperature however means longer to warm up and more power used to pump the water round the house.
I would go for very hot water for the radiators and insulate the pipes that carry the water( insulate both before and after the radiator) and tap water that is at the most used temperature with a kettle on standyby.
But it is a suck it and see situation really.

But if you want to save money, then insulation, insulation and then more insulation is the best way. Followed by dropping the temperature of the house and a woolly pulley.


Established Member
For the radiators there should be a 50 degree temp difference on flow and return of the boiler aim to get flow at 70 and return at 20 (this is optimum, you may not get this depending on the size of your system)

Start with a cold system and shut the manual side of all you radiator to off and the thermostats to max. Then start the boiler and open the manual valve on each radiator slowly until you feel a temp rise in the radiator. Then set the thermostat on each radiator to desired temp.

Hope this makes sense.


Established Member
Why did installing a smart meter send the bills up?

If your system has a header tank, you need to make sure the hot water is at least 55 degrees to avoid the risk of infection from the header tank. Can you measure it with a thermometer at the tap? If your system has a pressure vessel instead, which will be a bulbous tank, usually red, near the boiler with a pressure gauge, there's no need to worry about the 55°. Other than that, turn down the hot water temperature until someone complains of not enough water for a shower or not hot enough for dishwashing, then turn it up a notch, job done.

Given the system is 'eco', the boiler must be condensing. If so, the lower the temperature of the water in the heating system, the better. Just keep turning it down until you get cold, then turn it up a bit.

Putting thermostatic tops on the radiator valves will always help. If the system is newish, they will simply replace the existing, and can be done without getting wet: the old valve tops should screw off with the knurled hand-nut, and the new ones screw on. If it's a brass nut that needs spanner on an old valve, don't do it!!


Well-known Member
What temp should i be setting the tap (should it be just below scalding temp) and what setting should the rads one be set too ??

The house is a 2 bedroom 1930's terraced house (4 connecting houses that the 2nd and 3rd house are separated by a alley but joined at the upper wall)

Jean Valjean

It depends on how well your house is insulated in answer to your question. I have come across 1890 houses that are really well insulated and 2010 that are rubbish.

Most people really dont understand condensing boilers and apply the old rules of conventional boilers to them instead of using them correctly.

If you look at the front of your boiler manual where the specs are, you will see that your given heat out put for gas burnt gets higher as the boiler is run cooler.

This means that in a well insulated house it is cheaper to run the boiler for longer at a lower temperature, than to run it shorter at a higher temperature. As the higher the water temp the less condensation heat transfer takes place and the lower your heat output from the gas you burn.

Of course if you have a poorly insulated house then the boiler can run for so long, that this saving is lost.

The same applies with the hot water, set it at the lowest temp you can live with.

In regards the temp of the flow and return at the boiler their should be between a 10 to 20% temp difference, more than this will cause your boiler to work harder and cost you more gas as a result.
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