Another CH question

[Broadback]

I asked a while ago if it was worth replacing my combi boiler and received superb advice, so here is another question. I have rad stats on all radiators except the bathroom. The installer said that if that went off the water could not circulate and damage the system. Now is it worth installing a bypass and a room stat, or a rad stat for the bathroom? If so where on the net can I get the necessary information n installing such a bypass?

[newshound]

Modern boilers seem to have a built-in bypass, you can download manuals for most things from the net to check.

[John Rumm]

Do you have a room stat at the moment?

If not, then it would seem sensible to add one. In which case you could add a TRV to the bathroom rad, and then remove the TRV head from the valve in the room where the stat is situated.

[harryagain]

The purposeof the bypass is twofold.

1. It allows water to circulate so that the boiler thermostat gives proper control and the boiler works at it's most efficient.
2. It maintains constant pressure in the system. Without, as the TV valves close, the pressure (derived fromthe pump) rises so tending to defeat them. The bypass is ajustable and should be adjusted so it is just closed when all the TVs are open. This allows a constant flow of water through the boiler and also the pressure in the system remains more or less constant so allowing the TVs to work correctly.

So it enables constant volume through the boiler and constant pressure on the radiator system

[John Rumm]

It can be counter productive with condensers, since it raises the return temperature and reduces condensing efficiency. A smart pump would probably be a better bet if you are going to tune the system to the point that all the TRVs shutdown before the room stat is satisfied.

[harryagain]

There is an optimum flow through a boiler for maximum efficiency. This why modern boilers have pump and bypass within the cabinet all pre set up. Prevents the cowboys from fitting unsuitable items.

[John Rumm]

*Some* modern boilers have pump and bypass (they are called system boilers or combination boilers). Heating only boilers without a pump are still readily available.

Of those, most have the pump speed set, but the valve is manually adjusted during installation.