How can I tell if my existing gravity fed CH system has a radiator bypass fitted?
I'm fitting TRVs and don't want to get into the situation where all the TRVs shut but the pump is still trying to push water round the radiators.
sponix
What do you mean by "gravity fed" - vented, as opposed to sealed/pressurised - or do you mean that the hot water circuit uses gravity/convection circulation rather than being pumped?
How many (if any) motorised valves are there - and are they 2-port or
3-port?Does your system layout fit any of the 'Plans' in
If so, which one?
vented, no motorized valves
Probably the first one would be the closest...no zone valve though but a non return valve instead.
sponix
If you've got a gravity HW system and pumped CH system with no motorised valves, you've pretty certainly haven't got a by-pass - and you don't need one. A by-pass is only needed when the boiler needs to keep the pump running for a bit after it has stopped firing, to stop it overheating - and the water must have somewhere to go if all the zone valves are shut. Your boiler is quite happy to heat just the HW, without the pump running at all, so it obviously doesn't have this problem.
The pump needs to be controlled by a room thermostat located in a room whose radiator *doesn't* have a TRV. The pumped water always has a path through this radiator.You may need to throttle the lockshield valve a bit to make sure that the room with the room stat doesn't get too hot too quickly and shut the system down before the TRVs in the other rooms have had a chance to do their thing.
While you are modifying the system, you really ought to convert it to at least a C-Plan by fitting a 2-port zone valve and cylinder stat in the HW circuit, and wiring it as per the Honeywell diagram. This will save a lot of energy by shutting the boiler down when HW and CH demands are both satisfied.
What I'm worried is someone will close fully the valve on the "bypass" radiator, rather than use the room stat.
sponix
Set it right, and put a lockshield on both ends.
Good point!
Many thanks to everyone who helped.
sponix
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