pump overrun - how important?!

[andy1020]

Hi folks,

just had a boiler fitted (glowworm flexicom 18HX regular condensing.) It should have a pump overrun fitted acordging to glowworm.

Question is will it damage the heat exchanger if there's no pump overrun? Or is it just a 'recommendation' that isn't really too vital?

(Think I already know the answer but would love a few opinions.)

My installer seems to have done a good job otherwise and is coming tomorrow to finish properly (he ran out of time when fitted) as it's cutting out regularly which I think is because the bypass valve isn't open at all and needs adjusted to help with temp flow control. (It's old open vented system with some microbore too so reckon temp difference too great or flow too slow so open bypass a bit?? Opnions on this welcome while i'm at it, although i'm confident the installer will sort no problem)

Also, the old system just had a feed (L, N & E) to turn the boiler on from the control system when needed, so there's no permanent supply to the boiler or link from boiler to pump. So to fit pump overrun we'd need new permanent supply to boiler as well as live feed from boiler to pump, right?

So I was thinking the existing control feed from controller to boiler goes past the pump under the floor, so in theory if a new permanent supply to the boiler was fitted (not too difficult) then you wouldn't need both the L & N from the control to boiler, only a L to switch boiler on, so the not required N wire that did go from controller to boiler could be used instead as a live feed from the boiler back to the pump for the overrun, eliminating the need for new wire to be run from boiler to pump ( bit of a pain to run) Yes, it's bad practice due to wiring colours but otherwise would work?? I'm guessing folks might have done this before, no? Any opinions on this idea??

Thanks folks..

 

[GuessMan]

I'm sure GW just asked for it to inconvenience you.

When driving your car, why take your foot off the accelerator? Why not leave it jammed on and control your speed with the ignition key?

 

[Jordon]

Yes it needs a over run, no its not to inconvenience you, and yes its to stop the hex getting stung at the end of each run so pulls the heat away. If its cycling then the bypass will help dut also make sure the system is clean, as blockages will make the boiler struggle.

 

[Andygasman2010]

It needs an auto bypass valve and the pump needs to be wired back to the boiler as per manufacturers instructions. Also make sure it has a permenant L-N-E and a switched live from the wiring centre. Again - as per manufacturers instructions.

If it's not done like this you can get problems and it will potentially invalidate your warranty.

 

[transam]

If there was a problem with existing wiring ?? why fit a boiler that requires a pump over run ??? there are boilers that do not require it !!

In principle a pump over run could be provided via a pipe stat , but GW & other manus (?) would not except it .

At present GW would probably not except any in-warranty claim on the boiler!!!!

 

[andy1020]

ok thanks folks!

So need to fit pump overrun that's what I guessed.


transam-Reason for fitting this boiler we were limited by size to fit in so went for this one as fairly small. (and seems nearly all new condensing boilers need overrun)

On the wiring- no problem with existing just didn't have pump overrun, only live feed from controller to turn on boiler. Yes was talking about controlling pump overrun from boiler (not a stat or anything else) question was would it all work connected like i suggested?

ie:
New permanent mains supply to boiler (which can be used to run pump overrun from boiler as per manuf instruc.)
Old existing feed (had L&N) from controller to boiler altered so the live is the feed from controller to boiler (no neutral needed as boiler would have a new supply of it's own) and the neutral which went from controller to boiler rewired to become the live feed from boiler to pump for the overrun. (as per manuf)?