Should I have a bypass valve?

[diyer56]

Hi,

I was wondering if someone would be able to advise me please? A new boiler was fitted to my central heating system around 2 years ago by British Gas. The new boiler is a Worcester and, unlike the boiler it replaced, has a pump overrun feature. Around a year later the pump failed and this was also replaced by British Gas.

However what I am concerned about is that when there is no call for CH or DHW both motorised valves close and the boiler shuts down, when this happens the pump continues to run (as it should) however, where can the water 'go'?

I have attached a diagram to explain the setup.

View media item 69970
Should there be a bypass valve fitted around one of the motorised valves to allow the pump overrun to function? If so where should I fit this within the diagram?

I have noticed that the F&E tank has been overflowing and I was advised by a plumber to increase the height of the expansion pipe. I have completed this work but I was wondering if the pump pushing against two closed valves could cause water to overflow into the header tank?

 

[gas112]

have a look at boiler instructions it may have a built in one .

 

[diyer56]

Thanks gas112.

The boiler is a Greenstar Ri. I have downloaded the installation manual from here:

http://www.worcester-bosch.co.uk/ca...reenstar-ri--manufactured-from-april-2013.pdf

The install diagram for an S plan layout shows a bypass valve is required:
View media item 69977(F on this diagram)

Therefore it looks like this was left out by BG. I guess this hasn't helped my pump's lifespan?

Can I add one of these?
http://www.screwfix.com/p/drayton-a...=Search-_-SearchRec-_-Area1&_requestid=108760

Or am I better with a cracked open gate valve please?

The easiest place for me to add this would be to take a pipe directly after the pump and link this after the output from the DHW cylinder coil as these pipes are easily accessible. Would this be OK please?

Thanks again.

 

[Madrab]

Although I wouldn't hold out much hope, I'd get in touch with BG and see what they've got to say about it. They have incorrectly installed the system therefore I would say you have recourse with them over it.

Yes, without some form of bypass, then the pump is pushing against a closed system when both valves close and it will shorten its lifespan.
Using an autobypass valve will be more efficient than a gate valve that is open all the time. An open gate valve has to be finely balanced to avoid losing flow to the rest of the system.
Ideally the autobypass should be on the flow after the pump, before the zone valves and onto the main return pipework to the boiler after the rads/cylinder. Anywhere with that configuration would be suitable.

 

[D_Hailsham]

British Gas failed to install the required bypass, so they should be installing one at their own expense.

The lack of a bypass would be the reason the original pump failed, so I would insist on a replacement pump as well as the bypass. Otherwise you will be forking out for a third pump soon.

 

[diyer56]

Thanks both for your replies. Unfortunately the BG work was completed prior to my ownership of the house and therefore I don't have a claim against them. The crazy bit was although the boiler was a chargeable replacement the pump was replaced under the BG HomeCare system. You think they would have fixed the oversight at this point wouldn't you?

I will get the auto bypass installed.

Could the overrun of the pump against the close valves cause an increased water height in the F&E tank (either through the expansion pipe or the feed) despite both these connections being before the pump?