I’ve a heating system with that. The thermo switcher switches only the circulation pump. The old lady who owns the house alway s switches off the pump (take the thermo switcher to 10 Celsius degrees, therefore the pump won’t be switched on) Is it good for the heating system? Is it possible, that therefore the reliance 501 heater takes more gas to make the house hot?
I take it your system is what we call a “wet system” i.e. water based. Given that it is the system works best and fastest with the circulating pump operating which forces water through the heating radiators. Without the pump going it will rely upon pure convection currents which will work albeit a lot slower. The short answer to your last question is YES it will cost more to heat without the pump working. Hope this helps.
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