Vaillant VCW 20/1 T3 W System Bypass

[gorselands]

Hi, help needed identifying parts.

Small leak when boiler off from what appears to be the system bypass, (3 screws, diaphragm, spring, 2 union nuts,) located under pump. I assume from the slightly brown sticky leak that diaphragm has perished.

Seems a fairly straightforward job if I can get the parts/numbers.

Not sure what bypass does or why it only leaks when boiler off - unless it's to do with expansion/contraction. Heatingspareparts.com show it on their parts diagram but with no ref. numbers other than 2 packing rings (washers?)

Any help much appreciated,

Thanks Mike

 

[Bunnyman]

You can replace this old type with 150216 vaillant part number try here change the hole valve it's cheap enough you can't mend the old type http://www.partscenter.co.uk/en/hea...ll-ranges/vaillant-150216-by-pass-valve-30437

 

[gorselands]

Hi Bunnyman, thanks for getting in touch. Good to hear from you again. (Even though it's a sign something has gone wrong.)

So the right angle tube + something http://www.heatingspareparts.com/Content/images/spareparts/150216.jpg has replaced the the round bypass with diaphrahm. If you have a moment could you tell me what it's there for?
The link you sent has the part at £34.14 and HSP Direct Heating Spares at £2.65 +vat a bit of a difference http://www.heatingspareparts.com/Boiler-Spares/PartNo/150216 Both say they are genuine vaillant parts. Any comment?

Will try to get one locally, if not order one and will leave doing it till New year unless it's not wise to leave it - the leak is only small but as I said not sure what it's there for.

Cheers for now

Mike

 

[gorselands]

After Googling found out that the bypass valve provides a means to discharge the pressure should all the rads be turned off by the TRV's. I have always left a rad with no TRV "Always on" and in a room I don’t use that much. (it's the only rad with no TRV) As a bypass is fitted, Would it be ok to turn off that rad or is it still a good idea to have an open rad in the circuit? – Just thinking of the gas bill.