HW/CH Isolation valve for rad return

[wraymando]

Hi all,

Hoping to be a super quick question but for some background, with just HW on my rads start to heat up. I took the motor of the valve and switched manually with no luck but never really paid any attention to the smaller 15mm pipe that you see in the middle of the picture with an isolation valve circled in blue. That was neither open nor shut and sat somewhere in the middle. Now I closed that valve fully and then went back to manually changing the HW/CH valve and success!

The questions are is that a CH return pipe? Should it be open or shut?

In case it matters the flow direction is down from the pump (old school air separator sits just above) so when that valve is open it is able to flow somewhere.

 

[Exedon]

.That's a manual bypass if your boiler requires a system bypass a auto one would be better.

 

[wraymando]

What's the use case for the manual bypass? I guess I'm more checking with it fully closed whats going to happen (or not happen)?

 

[CBW]

It could cause leaks, by putting unnecessary stress on the pipes etc. It’s used to ensure a constant flow of water around the heating system. If not, then you’re heating water up, and when the heating has stopped (satisfied) then the pump has nowhere to send the water and dissipate the heat.

 

[wraymando]

Excess pressure! Cool so I guess if all the rad valves were shut prevents dead heading and things like that then too? I'll gradually open it up but given how open it was does that seem the likely cause of rads heating up on HW only (e.g. reverse flow)?

 

[Madrab]

reverse flow

That would normally only be the case if the last return wasn't from the HW primary. There is no real need for a bypass on that system unless all the rads have TRV's?

Heck of a place for a filter to be fitted too.

 

[wraymando]

Heck of a place for a filter to be fitted too.

Boiler location was awful, the house needs quite a bit of rework so really was just wanting to keep everything ticking along for a year or two and thought it was better than nothing!

Not all rads have TRVs but some of the previous DIY has left me questioning what's gone on (not just plumbing!).

 

[Madrab]

Certainly better than nothing of course, ideally though it wantsd to be on the return and as close to the boiler as possible. Is it a modern HO boiler and is the system water (rads) clear?

If not all the rads have TRV's then that valve isn't really needed and you can run it closed as there will always be a flow channel open when the pump over-runs ( if it's connected as such). Therefore the pump won't ever be running against a closed head and there will always be circulation through the boiler to dissipate any residual heat.