On Tue, 22 Nov 2011 22:04:12 -0000, The Natural Philosopher wrote:

Lieutenant Scott wrote:
On Tue, 22 Nov 2011 09:01:47 -0000, The Natural Philosopher
wrote:

Ben Blaukopf wrote:


However, even if the valve is faulty, if the timer is off then the
pump should still be off,

No.

thermostats and timers drive the valve, the valve has the high power
contacts that drive the boiler and pump.

High power contacts? Surely the current required for a pump and the gas
solenoid etc in a boiler are not "high power", and could be driven
directly from the stat?

start up power for the pumps is quite high.

Everyone does it this way...I guess there is a reason.

The valves have what look like 5A capable microswitches.

Thermostats are much more delicate..well SOME are. Timers also.

I think the rationale is that is not a good idea to have - say - a
motorized valve and a pump in parallel..if the valve goes the pump sits
there pumping into an blocked circuit.

Yes that makes sense. Just had a look at mine as I'm about to add another radiator - see below. It is wired as above.

I can see another reason for doing it this way. I have two switches in the house - one is for hot water, the other (which is now a thermostat) is for the radiators. If these both switched on the pump directly aswell as the valves, then power would jump across to the wrong valve and they'd both always open, unless the switches were two pole.

The thing is I have never got a bimetal roomstat that will accept the turning on of the motorized valve. I always get an arc in the stat at switchon, which often prevents switchon. I had to get a digital one (with a relay in it). The valve is marked 50 watts. I assume this is the rating of the motor.

Ergo the normal thing is that the
valve is open BEFORE the pump starts..you hear the whirr...the boiler
light goes on..the pump starts,...and then the boiler fires.

I wondered why the boiler didn't start immediately. I guess the motorized valve takes a few seconds to move.

As for the extra radiator - it's in the garage - this will be fun :-)

I'm intending to attach a third motorized valve, which will mean there are three independent pipe circuits, one for the hot water tank, one for the radiators in the house, and one for the garage radiator(s). So any one or any two or all three can be on at once. Easy enough as all the valves and the big ass electrical connection block are in the loft right next to the hatch. The "fun" will be threading the insulated hep pipe through to the garage (there is already quite wide conduit for a wire and the pipe to the tap). I'll have a thermostat in the garage, and one in the house. So the heating will control itself. I just pick two temperatures and leave it forever.

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