Pump Bypass

[CIB]

All

I am partly updating my central heating system. The only bit that I am stuck with is the need for a pump bypass.

If I use a mid position valve, do I need one? The boiler ( a Halstead Hero 60) has a pump overun feature. The installation instructions talk of a 7 litre bypass loop, even with a mid position valve.

My understanding was that there would always be a flow routewith a mid postion valve, so no bypass was needed.

Am I wrong?

If I am, shal I plump in a bypass radiator, or an automatic valve

CIB

 

[JohnC51]

See my thread "Water boiling in the heating system" as I too have concerns about bypass valves - mine is manual and without it my system would have blown by now.
I have seen Glow-worm instructions stating that a bypass is a "must-have" and that it should never be closed under any circumstances, so i guess the advice has to be to install one!

I've found that the boiler stat is in the return path so, which gives the possibility of the flow getting ridiculously hot unitl the return temperature is sufficient to switch off the burner.

Some of the experts out there will give sounder advice I'm sujre. Good luck!

 

[ChrisR]

Somewhere on this forum there's an excellent description of what a 3 port valve does. It turns out that in the normal course of events the valve can be left open to the heating, which isn't what you might expect of a spring return valve. Yours may not BE a spring return one anyway!

So if you have trv's they could all be shut to give no flow at all throughthe boiler. But if you have a radiator without a trv, which is never turned off, that will do as a "bypass". 7 litres is more than will be in the pipe to the HW cylinder too, but that's quite a good dumper of excess heat, so I'd have thought it enough. But I have to advise you stick to the mfrs instructions. Regs now say you have to put an Automatic Bypass (spring loaded) on new systems unless the boiler mfr says otherwise.