New system, HW on only but rads getting hot!

[DP]

"The CH valve has been replaced now so that should be OK." Headless chickens strike again.

How would I test for reverse circulation? The cylinder return goes through the floor, down the wall parallel to the boiler and then T's into the primary return, the closest return to the boiler though is the CH return T.

Your installer as well as WB engineer do not know their basics. Water that is returning from the cylinder passes CH tee before enetering the boiler is your problem. First tee in this installation should be to and from the cylinder.

 

[JDLDIY]

"The CH valve has been replaced now so that should be OK." Headless chickens strike again.

How would I test for reverse circulation? The cylinder return goes through the floor, down the wall parallel to the boiler and then T's into the primary return, the closest return to the boiler though is the CH return T.

Your installer as well as WB engineer do not know their basics. Water that is returning from the cylinder passes CH tee before enetering the boiler is your problem. First tee in this installation should be to and from the cylinder.

Methinks I may have misled little bit here, please bear in mind that I am the non-technical piece in the loop and I may not be the most accurate in describing what has taken place. Thing is that I am the one with internet access!

Initially the primary flow pipe was getting hot and is not now as the plumber diagnosed the CH valve as faulty and replaced it. The installer was probably more certain of this than I have led you to believe. The source of heat to the rads is now coming from the return side and so we were interested to see whether anyone else had fitted this boiler and had experienced similar problems....

Initially the HW return was T'd into the CH return upstairs, but that has now been brought downstairs and is now T'd into the CH return close to the boiler. At the same time they found that in the electric installation brochure it mentioned in passing a 22mm bypass should be fitted and so this was also done.

The installer is now on a family holiday and intends to come back to sort out any probs when he returns. Meanwhile I said I would do as much research as I could to help out. Tinkering over the last 2 days I have found that the system works much better, but especially with the bypass valve (which is a gate valve) closed off. If I open the gate valve the flow reaches the downstairs radiator circuit and heats up the first couple of rads. I can close off the gate valve to stop this but what function should a bypass perform exactly?

What hasn't helped is that the WB literature (installation and user instructions) concentrates on the combi versions of the range and the system boiler remains unexplained. The user instructions are particularly bad and really don't cover the system boiler at all, to the extent that some of the controls on the boiler would seem to apply only to a combi, so are a total mystery.

JD

 

[ChrisR]

Really do need to see a layout to comment more but, traditional purposes of bypass is 2 or 3 or 4 fold.
1 to allow boiler to circulate water when all valves are shut. Othrwise heat exchanger etc could overheat and distort - especially an ally one like yours
2 to allow water to circulate through the boiler so that IT can regulate its own temperature

3 to regulate the temperature drop across the boiler as trv's close

4 to stop trv's making a racket as the pressure across the last one to close goes up


Mfr will have done some homework on which of 123 are important, so DO follow their instructions closely. Baxi haven't done h/w on some of their boilers and they can't decide where the ABV thing shuld go, but I digress!

An ABV won't open at all unless the flow goes down in the system such that the pump pressure goes up. Bin the gate valve and install an ABV - unless I suppose the mfr insists on a gate valve! Actually I'd call them if in doubt.

There is good reason to put an ABV at the far end of a system, but boiler mfrs don't seem to realise. If you turn it to say 3 bar near the boiler you're reducing the head available to 3 bar from say 6, whereas if its far away you aren't - there would be a drop getting to the abv - but the flow can still happen.

Another advantage of an ABV is that it has a spring against a seat so is also a non-return valve which a gate valve isn't. When the pump's off there's no gravity circulation through it.

Get an ABV
On offer at the mo at bes.ltd.uk/ Less than £20 including their carriage.

Adjusting an ABV is easy - check pump characteristic curve for thehead for the flow you need (assuming thats stated) and find the head drop through the boiler and pipes at that flow. Add up and adjust valve accordingly.

 

[DP]

I would have three tees on the flow and return. Nearest tee to the boiler would be your bypass, next tee flow and return for the cylinder and final tee CH circuit.

You are getting reverse circulation. Water that is flowing in the return to the boiler is making its way across and up the returns of some of the rads when HW demand is in place. To relocate the HW return past all the CH returns should stop this. Also ensure convection does not take place by placing the HW tees in the drops as opposed to on the horizontal runs.

Ensure bypass loop length is as specified.