revtothelimit - motorbike forum

I think the tank heating worm circuit needs to be restricted a bit, to encourage water from the gas boiler to go through the radiators.

I can only see a motorised valve in the tank heating circuit, beside the tank. Can they be restricted from fully opening?

Have I got to get off my arse and take a photo of the valve?

I'm not sure your problem is that simple, it should heat the tank and switch to just radiators.
Why is your tank not getting hot enough to switch HW off? The first thing I'd look at is the thermostat stuck to the tank, if it's above 60 then turn it down.
Usually HW and CH can be timed independantly, are they correct?

The tank thermostat is turned up high. Mrs likes it that way.

Yes they’re timed separately, but we generally want hot water and hot radiators around the same time.

Mussels wrote: Sat Dec 06, 2025 9:46 pm I'm not sure your problem is that simple, it should heat the tank and switch to just radiators.
Why is your tank not getting hot enough to switch HW off? The first thing I'd look at is the thermostat stuck to the tank, if it's above 60 then turn it down.
Usually HW and CH can be timed independantly, are they correct?

There can be two aspects to the limpet type external thermostats. The position on the hot water jacket can determine how much hot water is stored before the radiators take full priority. Put the thermostat higher on the tank and less water will be immediately heated but might not be available for (say) a bath. Setting the temperature on it does as expected. The other controls vary enormously. The main controller might allow times to be independent for heating and hot water ( hence the motorized valve which is most likely to turn off heating on the primary circuit ) and the boiler itself will have a thermostat controlling primary circuit temperature and hence radiator temperature directly. The condition of the boiler and pipework can play a big part especially in older systems and some very odd configurations crop up too.

Blocked radiators are very common and a more likely reason for poor heating.

JackyJoll wrote: Sat Dec 06, 2025 10:13 pm The tank thermostat is turned up high. Mrs likes it that way.

Yes they’re timed separately, but we generally want hot water and hot radiators around the same time.

To get both circuits heated at the same time you will need a thermo valve with a midpoint function/setting, otherwise it's either DHW or CH, but not both at the same time.

Thanks all; interesting stuff.

I wonder if part of the problem is the tank heating circuit is all 3/4” copper, while there’s a lot of 1/2” in the radiator system.

mangocrazy wrote: Sun Dec 07, 2025 12:37 pm

JackyJoll wrote: Sat Dec 06, 2025 10:13 pm The tank thermostat is turned up high. Mrs likes it that way.

Yes they’re timed separately, but we generally want hot water and hot radiators around the same time.

To get both circuits heated at the same time you will need a thermo valve with a midpoint function/setting, otherwise it's either DHW or CH, but not both at the same time.

The same can be achieved with two 2-port valves with a two channel time clock, cylinder stat and room stat, one for the DHW, the other for the radiators. My hot water is timed to come on before heating so tank is brimmed with hot water* before boiler becomes dedicated to heating.

*hot water stays hot in the tank for hours so no need to heat it at the time it is needed. Mine is set at 54°C and has an anti-Legionnaires setting heating it to 60°C once a week.

JackyJoll wrote: Sun Dec 07, 2025 2:08 pm Thanks all; interesting stuff.

I wonder if part of the problem is the tank heating circuit is all 3/4” copper, while there’s a lot of 1/2” in the radiator system.

Make sure the tank and pipe work is lagged and adjust the timer on the water to an hour in advance of the radiators.