What's this pipe? CH / HW setup
- Thread starter BigChin1
- Start date
Your current labels must be wrong? Otherwise your hw and ch are plumbed together which would be odd, not work and dangerous?
Looks like all those pipes are ch flow and return so that pipe is probably some sort of bypass.
Looks like all those pipes are ch flow and return so that pipe is probably some sort of bypass.
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Looks like could be right to me but difficult to confirm without seeing more, I assume what you have labeled as boiler flow just goes up and back down to pump. And yes that will be a bypass and should be open very slightly, nowadays auto ones are fitted instead. As for the above post, boiler primaries don't actually mix with the water that is drawn off.
You would never have direct hot water and CH circuits linked - the result would be unsafe and toxic compounds in the hot drinking water.
I’m not an expert just our old system had this.
Your system looks like our old one. We had a 25 year old boiler, open cold and hot water immersion tank. The CH pump had a couple of valves and a bypass between supply and return - iirc it allows some of the pumped water to return back to the boiler. As far as I could figure out it is tuned as part of the radiator balancing. It also allows the pump to not have too much back pressure.
The two circuits are likely to be - CH and hot water tank coil circuits. The HW coil then heats the water in the immersion tank in addition to the electrical immersion heater element.
I’m not an expert just our old system had this.
Your system looks like our old one. We had a 25 year old boiler, open cold and hot water immersion tank. The CH pump had a couple of valves and a bypass between supply and return - iirc it allows some of the pumped water to return back to the boiler. As far as I could figure out it is tuned as part of the radiator balancing. It also allows the pump to not have too much back pressure.
The two circuits are likely to be - CH and hot water tank coil circuits. The HW coil then heats the water in the immersion tank in addition to the electrical immersion heater element.
Last edited:
Yes that's correct.
Correct. Just out of shot on the right-hand side is the hot water cylinder. HW flow and return are the coil. Should have mentioned in the original post my system is vented Y-plan, regular boiler, with feed & expansion and cold water tanks in the loft. HW tank has a backup immersion heater but not used.
Thanks to you both for explaining the purpose of the bypass. It makes sense now with the behaviour I was seeing. After measuring the temp of the various pipes, the flow pipes would be around 68 degrees (exactly what the boiler said) and the CH and HW return pipes would be somewhat lower, as to be expected. But the Boiler Return was considerably hotter than those, not far off the flow temp. Having now checked the valve on the bypass it was almost fully open, so have turned it almost closed and now the boiler return temperature is closer to the CH/HW returns. Radiators are also heating up faster.
Just did some Googling and one of the reasons for the bypass is if every radiator is fitted with a TRV and they all close, there needs to be somewhere for the water to flow. This was the case when our house was built, but now we only have TRV's on the upstairs radiators, so in theory it shouldn't be a problem to close the bypass.