hot water cylinder by-pass valve replacement?

[tellme_why]

Hi,
My S-plan has a by-pass valve (common plegler gate valve) that seems incapable of closing the flow (see red circle of the diagram).
I tried to close it completely, turning until the end but the output pipe did not get colder, at touch seems the same temp as the input.
I suspect some crap was deposited in the bottom?
How can I tell whether it's actually closing properly??
Replacing it is a one-day job because it's very fiddly because it's behind the hot water cylinder, so would like to avoid it.
I wanted to replace it with a ball valve so I can tell for sure when it's fully open or partially closed.
I want to make sure that the by-pass pipe does not get too much flow and the hot water cylinder gets its fair amount.
I suspect too much water flowing in the bypass because the how water cylinder takes a lot of time to heat up.

Any suggestion whether I should replace the valve or some way to confirm that the valve is actually working and I can use it to balance the by-pass circuit?

Many Thanks

 

[Johntheo5]

You should get ~ 3 full turns betwwen fully open/shut, if still hot then new valve required.

Are you using this as a bypass because of all the rads having TRVs?, you can use the (yellow) coil outlet valve to balance your HW cylinder, although this is now frowned on I think, you can programme the HW on for say a hour before CH required, any topups required will then not be too long and won't have a huge effect on the CH even if both then programmed on together.
A manual bypass, even though simple means bypassing when not required with the TRVs throttling up, you could consider a ( ABV) automatic bypass valve, depending on pump mode/setting, what is your pump make/model/mode/setting?.

 

[tellme_why]

Thanks; the red valve was there before TRVs were invented I think, so must be a std feature of S plans. My concern is that the stuck open bypass prevents full flow to HW cylinder making it inefficient. I always operate HW on when CH is off via stat and electric 2 ways valves.. If I replace it, is the auto bypass reliable? It’s very difficult to replace so thinking ball valve would be better than gate valves?

 

[fixitflav]

Thanks; the red valve was there before TRVs were invented I think, so must be a std feature of S plans. My concern is that the stuck open bypass prevents full flow to HW cylinder making it inefficient. I always operate HW on when CH is off via stat and electric 2 ways valves.. If I replace it, is the auto bypass reliable? It’s very difficult to replace so thinking ball valve would be better than gate valves?

It might be worth starting from cold and seeing if it gets hot downstream of the valve quicker than you think it should.

In that position the valve is bypassing in CH mode as well as HW, so if it's not affecting CH there may not be much wrong.
Are you sure it's not just a furred-up cylinder coil? Mine is getting on for 25 years old and takes about 25 minutes to reheat after calling due to heat loss, without using any HW. I dread to think what state the coil's in but it doesn't give a problem in practice.

 

[Madrab]

Gate valves were originally added to CH, when systems became fully pumped and they were used as proportioning valves on the HW primary feeds to allow it to be balanced. When S plan came in, newer boilers and TRV's started to being used, they were employed to create a manual bypass, so when all the valves shut it would ensure a min overrun flow through the pump/boiler, now replaced by ABV's.

Can you access the same bypass pipework the gate valve's on? If so just leave the gate fully open and just cut in a new ABV where access is easiest.

 

[tellme_why]

Hi, I sorted it.. did proper measurement from cold using IR thermometer and the bypass keeps 10C difference in/out which is suggestive of no flow passing..thanks for your responses

 

[Johntheo5]

What is the IR temp reading on the flowpipe where the bypass is teed off, the temp say midway along the bypass and the temp on the return pipe at the bypass T?.