Whoever fitted the heating system put a pipe directly from flow to return (just to the right of the pump in the diagram above).
There's a gate valve on it with a red tap, which is switched off.
What is this for?
Whoever fitted the heating system put a pipe directly from flow to return (just to the right of the pump in the diagram above).
There's a gate valve on it with a red tap, which is switched off.
What is this for?
the garage both with their own motorized valve, which are irrelevant to the question).
(just to the right of the pump in the diagram above).
It's a crude bypass loop. It ensures there's still a flow path even if all the radiators shut off, and/or if the arrangement of valves for selecting heating/hot water have a mode where they're all closed.
It probably shouldn't be shut off, unless the system has been modified since the original installation and no longer needs it. You can get special bypass loop valves to use instead of the gate valve which only open when the pump is trying to push against a closed circuit, so they don't bleed any flow into the return when there's a real demand for heat.
In message , Lieutenant Scott wrote
The gate valve is probably turned on a tiny bit but possibly seized in this position now. It provides a bypass path if all the radiators get turned off.
A bypass valve is normally used these days
the garage both with their own motorized valve, which are irrelevant to the question).
(just to the right of the pump in the diagram above).
Ah I see, thanks.
It's possible I shut it off years ago and forgot.
It used to be on a timer, and only limited by the thermostatic valves on the radiators, so it could block the pump without it.
But I added a room stat and opened the radiator valves fully, so there will never be a blocked pump.
I'll leave it shut for maximum power output.
Would a pump actually break with no flow?
If so, what is the minimum flow required for the average pump? I could have the situation of only having one 10mm HEP pipe flowing (the garage circuit).
the garage both with their own motorized valve, which are irrelevant to the question).
(just to the right of the pump in the diagram above).
Well, it would do if the gate valve was open a bit.
radiators, so it could block the pump without it.
never be a blocked pump.
Ideally, remove the TRV in the room with the stat, so it can't get turned off. You fit a stop valve instead (no knobs to turn).
No, but the boiler's heat exchanger would - it would overheat.
the situation of only having one 10mm HEP pipe flowing (the garage circuit).
You need to look at the boiler's instructions. The minimum is usually given as the minimum length of pipework around the bypass loop, so it's enough to absorb the heat still passing through the heat exchanger after the burner switches off, without causing the overheat stat to trip or the water in the exchanger to boil. Some modern boilers don't need an external bypass loop.
radiators, so it could block the pump without it.
never be a blocked pump.
I tend to leave all my doors open, so the whole house is at the same temperature.
I'd have to accidentally turn off six TRVs to cause a problem.
Mind you in the garage, only one (non thermostatic) valve. But its quite a number of turns, you couldn't knock it off by mistake.
[ignore this line, I see you answered it below] Surely the boiler would just cut out when it reached the desired water temperature and stay off, as it already does by cycling on and off to maintain the correct temperature in the flow pipe.the situation of only having one 10mm HEP pipe flowing (the garage circuit).
If it's just to remove that little bit of heat, I would imagine the flow through
10mm HEP would be sufficient.Hang on a sec. If I switch off the heating at the point where the boiler is just about to stop burning, then no water is being pumped, and things don't break.
One day, someone else might be living there.
number of turns, you couldn't knock it off by mistake.
the situation of only having one 10mm HEP pipe flowing (the garage circuit).
through 10mm HEP would be sufficient.
Might be.
just about to stop burning, then no water is being pumped, and things don't break.
The boiler probably has a run-on timer for the pump, to keep it going for a minute or two after the call for heat input has gone and burner has gone out.
It is customary to explain the heating system to the next owner. The previous owner did to me.
Heating the garage may well have to be explained, I don't think many people do that.
number of turns, you couldn't knock it off by mistake.
have the situation of only having one 10mm HEP pipe flowing (the garage circuit).
through 10mm HEP would be sufficient.
just about to stop burning, then no water is being pumped, and things don't break.
Not in this case. The boiler does not tell the pump when to operate. The pump and boiler are seperate units wired in parallel and go on and off together when the room stat / timer / whatever turns them off.
I would have needed a seance to do that in the house I live in.
Ah.
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