Bypass valve problem and question about CH manifold

[jonc123]

I've just installed a bypass valve on my central heating so as to avoid having to have a radiator turned on all the time.

I've installed a tee just before the 3 way valve input and another tee on the return pipe from the hot water cylinder, the bypass valve sits between the two. The directional arrow points from the 3 way valve end tot the cylinder return.

I've tried testing it as follows:
1. Controller set for Central heating "on", hot water "off"
2. There is a valve in the feed to the central heating circuit - I've shut that.

Unfortunately the pipe leading from the new bypass valve (to the return feed) does not get hot - so I'm concluding the bypass valve isn't working. In the scenario described should it be working?

I've another possible issue that I discovered while trying to troubleshoot the bypass valve issue. There are two pipes that disappear into the floor that only get hot if central heating is "on". As one gets hotter first (it leads from the 3 way valve), I'm assuming that this is the feed and return to the radiators. Under the floor must be a distribution manifold or similar. Here is the odd part (to my thinking): If all the radiators are switched off (via their TRVs), the two pipes mention still get hot. I don't understand why that would be so if there is no radiator turned on. Is it possible that there is a bypass valve (or similar) on the manifold?

Thanks in advance for any replies.

 

[Johntheo5]

If a OV (open vented) system then you should have the circ pump a short distance "back" from the 3 way MPV with its (the pump) arrow pointing towards the MPV, the centre MPV pipe then feeds either the CH or the HW coil INLET (normally the top cylinder coil), or both, not sure what you mean by this "The directional arrow points from the 3 way valve end tot the cylinder return."

Port B goes to the HW cylinder, Port A to the CH.

 

[jonc123]

If a OV (open vented) system then you should have the circ pump a short distance "back" from the 3 way MPV with its (the pump) arrow pointing towards the MPV, the centre MPV pipe then feeds either the CH or the HW coil INLET (normally the top cylinder coil), or both, not sure what you mean by this "The directional arrow points from the 3 way valve end tot the cylinder return."

Port B goes to the HW cylinder, Port A to the CH.
View attachment 392689

Sorry if I've not explained correctly. I'll try again. As you say, the pump is a short way back from, the 3 way valve. I've added a tee into the pipe between the pump and the 3 way. I've connected a bypass valve to the tee (with its directional arrow pointing away from the tee). I've added a tee into to the return feed (back the boiler) and connected the other end of the bypass valve to that tee. No matter what I try, the bypass valve does not appear to pass any water through it.

 

[Johntheo5]

Is it a ABV?, (automatic bypass valve) and if so what have you set it to?

 

[jonc123]

Yes it is an ABV. Tried it at max (0.5) and min (0.1) and everything in between.

 

[Johntheo5]

Thats strange, is the circ pump A rated with one of its modes, proportional pressure, PP, if set to a low PP setting it will back off with reduced flow but unlikely to be your problem, the pump is obviously running??, what make/model??

 

[jonc123]

Both problems solved.
I had a spare bypass valve, I fitted that and it works as expected. Unfortunately (for me) the spare valve was a 90 degree angle whereas the original was a straight through one - so I had to re-do the pipework. After I had finished I took apart the original pipework and discovered the culprit - a huge blob of sludge had lodged the original (new) valve. Having flushed the system beforehand I didn't expect such a large chunk to land in my new valve! The fact that the valve was mounted vertically with the input at the top probably made it worse.

The other problem I asked about regarding the manifold - I discovered a radiator that was still turned on. So once turned off, there was no further flow through the CH pipes that lead to the radiators.