Auto bypass necessary?

[PaulAH]

For the geniuses: A question about auto-bypass valves in a new boiler installation. System has 22 rads, two of them tiny (WC and shower) that could be left on permanently without a TRV. Hall (where room stat is sited) also has no TRV, deliberately. System is three zones wired for boiler interlock.

So is an auto-bypass
a) Necessary
b) A legal requirement
c) Anything else

The reason I ask, apart from curiosity, is that we’ve plumbed for a straight in-line valve only to discover that the Danfoss - the only one I can find that isn’t a 90 degree job - is over 60 quid. Angled ones are much cheaper but it would mean a lot of awkward new pipework as it’s in a tight spot.

Many thanks
Paul
"Day Centre resident"

 

[AlanE]

Number of rads. not really relevant and with three zones, presumably controlled by two port motorised valves, the number of rads without TRV's is also not relevant.

The purpose of bypass valve is to provide a path for the water where there would otherwise be none.

It is also a bit poiltless fitting one at the end of a radiator ciruit since when the valve controlling the rads is closed the bypass is isolated from the boiler.

The bypass should be fitted after the pump but before any motorised valves. What type of boiler and what do the manufacturers instructions call for.

Alan

 

[PaulAH]

Thanks for that, Alan

The bypass should be fitted after the pump but before any motorised valves

That's exactly where it is (or will be).

Boiler's a Boulter Camray. The manual (haven't got it to hand) makes a reference to avoiding situations where the water flow is halted while the boiler is still firing, as it can create damaging hot-spots on the heat exchanger. But I don't think it specifically mentions a bypass valve.

Presumably the bypass is there to cater for that freak moment when all TRVs are closed, room-stat is calling for heat, therefore boiler still burning, and water has nowhere to go. Seems unlikely.

Incidentally, the water in a car rad is called coolant. Anyone know an equivalent term for the stuff in a heating system? Heatant?

Regards
Paul
Matron's coming round with tea now.

 

[ChrisR]

Presumably the bypass is there to cater for that freak moment

Boiler probably has "pump overrun", when it will need a path to dump excess heat after the boiler is off and valves are shut.