Upgrading a gravity HW + pumped CH system...

No NRV's as far as I can determine... it's all on a single channel programmer to at the moment so when the system's on, rads & HW are heated.

Doesn't matter about whether it's winter or summer!

Also, only one radiator in the property is currently fitted with a TRV - but that's another project..
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An impeller type pump does not block through passage of water when it is switched off, just as a desk fan cannot prevent air passing through it when it is switched off.

Pumped heating systems without motorised valves had an anti-gravity valve [which was purpose-made and not the same as a non-return valve] fitted specifically to prevent the upstairs radiators heating when the pump was not running. This method is still used on two pump systems, typically in light commercial boilers, where it is simpler to use two pumps rather than one pump plus a diverter valve.

I do not wish to appear offensive, but you guys should not peddle guesswork as fact.
Thanks MysteryMan.

On this note, any idea why there'd be what looks like a normal motorised valve on the return pipework from the hw cyl...?
It is to control the heating of the hot water, and will be controlled by a cylinder thermostat. It may well be allied with a pumped radiator circuit with/without an anti-gravity valve. This can give fairly good control of a heating system based upon a heavy old boiler.

If you are changing anything, it is well worthwhile changing the system to a fully pumped Y Plan, as above. This goes on the flow rather than the return, and you need to remove the existing 2 port valve. It may be decades old anyway.

Fully pumped and thermostatic control are legal requirements on all new or upgraded systems now, and no modern boiler would be happy on gravity primaries.

Do please consider weather compensation, it really does work, in spite of what others have posted!
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Certainly interested to look into Weather Compensation - presumably WC can be fitted to an existing boiler by means of a controls upgrade ?
That depends upon the boiler.

Weather comp will make the boiler condense - that is where the energy saving comes from. This may wreak havoc on a non-condensing boiler.

Weather comp is best installed as part of a new high quality condensing boiler.
Boiler is a thermacon option 60/80 oil fired unit at the moment which we're not really planning on changing any time soon as it's only about 5 years old.

Sounds like we'll be doing a pumped y-plan conversion along with upgrading the controls and leaving weather compensation for another day.
NRV's are & were used to stop gravity circulation on pumped heating gravity primary heating system's !!!
They were not really the same as non return valves. Anti gravity valves are not spring loaded; non return valves are.

Back to the original enquiry:

You are probably best to leave weather comp until you do a boiler change. The saving on oil is much less than on gas - because there is less hydrogen and more carbon in oil.

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