Do I need a bypass valve or not ?

[davesch]

I'm just about to convert my CH system from Y plan to S plan. Currently I just have a 15mm gate valve bypass in the airing cupboard and that is shut as I don't have TRVs on all rads. The guy who installed my boiler said that was fine, just open it enough to hear a bit of water flowing.

However since then doing a bit of searching, some seem to say that an automatic bypass valve is a must, some say it depends on the boiler. I've checked the install manual for mine (Vaillant ecoTEC) and it seems that it already has a bypass valve and makes no mention of needing an external one. That said, I seen it stated as a good idea to still have a bypass away from the boiler. Do people agree ? and if so:

Should I install an auto valve and if so what setting ?
Does it matter whether the valve bit is vertical or horizontal ?

Thanks
Dave.

 

[lame plumber]

building regs require auto bypass on all new installs, choice is yours as long as there is a bypass available via rad at present and manual one you should be ok at present. cant hurt adding one if you want

 

[R1CKY]

Yes. Using a gate valve is not an accepted method anymore, plus you are just short circuiting heat through the primary flow and returns. Your boiler will probably have a pump overrun function. Which means the pump continues to run after the burner shuts off and the zone valves close, meaning it has nowhere to pump against. The manufacturer may invalidate the warranty if an auto bypass is not fitted.

As for setting it, fire the boiler up for a while, turn heating and hot water off, when both zone valves close, adjust the valve until you can feel water passing through it at a decent rate.

 

[Gray0689]

building regs require auto bypass on all new installs, choice is yours as long as there is a bypass available via rad at present and manual one you should be ok at present. cant hurt adding one if you want

Auto bypass don't work very well with modulating pumps it one fitted

 

[davesch]

building regs require auto bypass on all new installs, choice is yours as long as there is a bypass available via rad at present and manual one you should be ok at present. cant hurt adding one if you want

Yes, it's okay for the mo, but won't have a bypass via a rad when converted to S plan. The boiler does have an internal bypass, but is that sufficient to a) satisfy the regs, b) keep the boiler healthy on overun ?

 

[doitmyself]

building regs require auto bypass on all new installs,

Not correct.

Domestic Building Compliance guide 2010

If the boiler manufacturer's instructions advise installation of a bypass, an automatic bypass valve should be fitted and the manufacturer's instructions on minimum pipe length followed.

 

[Dan Masey]

I'm about to instal my vaillant ect tec 630 system boiler. Iv just got a honeywell strait bypass valve. Ill be fitting it anyway even if not needed. Probably best leave one or two rads without TRV. Especially in the room with the wall stat.

 

[davesch]

I'm about to instal my vaillant ect tec 630 system boiler. Iv just got a honeywell strait bypass valve. Ill be fitting it anyway even if not needed. Probably best leave one or two rads without TRV. Especially in the room with the wall stat.

By far the easiest way for me to do this would be to use a straight bypass valve to simply replace the current gate valve, but would it be okay if the 15mm pipework was kept with 2 15/22 reducers and the valve mounted vertically (with the red valve top horizonal) ?

 

[AWheating]

By far the easiest way for me to do this would be to use a straight bypass valve to simply replace the current gate valve, but would it be okay if the 15mm pipework was kept with 2 15/22 reducers and the valve mounted vertically (with the red valve top horizonal) ?

yes it should be fine.