C/H - Setting Auto Bypass Valve With Variable Speed Pump?

[Peter Hemmings]

Hi,

I have just changed my pipework and have added an automatic boiler bypass valve so the boiler (Baxi Barcelona) does not control the pump (pump stopped and started at beginning of heating cycle). This was required if no valve was fitted.

I have a energy saving pump (Alpha +) which varies speed with back pressure and want to manually set the bypass valve.

The valve information asks for information on boiler minimum flow pump head etc and to read across a graph to obtain the "setting" on my Honeywell valve.

This all seems to be a bit complicated and I have just noticed that the pump has 3 manual settings, the slowest is for "adjusting bypass valve"!!

How do I find the setting, do I run system until the all TRV's start shutting (IE system reaching stable operation at nominal temperature) then adjust the valve till it just bypasses and back it off a fraction?

The above is what I have arrived at doing some logical thinking, but I might be wrong!

Apologies for any wrong terminology.

Regards

[dennis]

The bypass needs to open when all the valves are closed. So close all the valves and then adjust the bypass so it closes and then back it off so it is open. You need to set the pump to its minimum speed when you do it so it doesn't slow down any more and fail to open the valve in normal use. I expect that is what the setting "adjust bypass" is for.

[Peter Hemmings]

snip

OK I will do that, thanks.

The reason I was not going to shut all valves was that I have 2 towel rads which are never shut/adjusted so I thought I would never get to the state when everything was shut!

I see that would be the worse case scenario and will ensure a flow across the boiler. The only minimum figure I can find on the Baxi literature is 3 litres/minute which seem quite low!

Yep, that's what I thought

Thanks

[dennis]

If that is the case you don't need a bypass.

Mine frequently has all the valves closed as it is controlled by 5 two port valves that shut whenever nothing wants heat, a bypass is essential then.

[Peter Hemmings]

Oooops .....

Mine is the same, I have 2 2-port valves (and the two towel rads are on one of the loops controlled by a valve), so I DO need the bypass.

Regards

[TheScullster]

"Peter Hemmings"wrote

Don't you have a zone valve controlling all flow to the central heating, or is this Baxi Barcelona supplying one heating circuit only and no h/w? If it has a zone valve upstream of the towel rads then the by-pass will be needed of course.

Phil

[robert]

Reading between the lines of the alpha + literature, if the boiler doesnt require a minimum flowrate then is there any need for a bypass valve ? The pump in automatic or constant pressure mode seems to cope with zero flow .

[Fred]

The bypass valve gave the pressure it opened on a dial. So I set it at a pressure where I knew the pump could still pump water round according to the pump spec sheet (at the minimum speed).