A question about valves

[wilro15]

So I have been told my system has a 3-way valve that can switch between HW or CH or both.

The valve has a lever on the side which is spring loaded. When I push it down the water goes through to both HW and CH. When I release it and returns to rest the water goes only to HW. In this state there is a bit of "play" in the lever.

There doesn't seem to be a way to make it go CH only. Does this mean it isn't really a 3-way valve?

 

[45yearsagasman]

The way it should operate is when there is a call for ch from programmer and your room stat is also calling(if you have one) is that the motor inside the valve will drive and open the ch port. If this is not happening then there are several possibilities as to why. Most common fault on 3 ports is a failure of the motor. If you have a multimeter and are confident in its use you can attempt to find the fault, otherwise a repair specialist should be able to diagnose the fault in a short time.

 

[echoes]

The levers on (most) 3 port valves are such that the valve is in the mid-position (HW + CH) when the lever is operated. Your valve should still go to CH-only when supplied with the appropriate voltages on the appropriate wires. The lever is mainly there to assist with draining/filling when the power is off.

I did have a Horstmann 3-port valve once which could be put manually in the mid or CH-only positions. Got replaced though.

 

[Space cat]

There doesn't seem to be a way to make it go CH only. Does this mean it isn't really a 3-way valve?

The lever can't do it but the motor can. A demand for CH drives the valve initially to the mid-position so that boiler water can flow from both outlets. At this point a switch inside the valve inserts a large resistance in series with the CH demand. This reduces the motor current to a low value; enough to stop the spring from driving it back but not enough to carry on forward.

To get CH only, you need a 'NoHW' output from your controller. This is a real voltage, not just the absence of a HW demand. If, and only if, the valve is already at the mid-position, NoHW will drive the motor all the way over to the CH only position. It will stay there for as long as NoHW is present, even if the CH demand goes off.

 

[D_Hailsham]

Read How a mid-position valve works

 

[wilro15]

Thanks for the info everyone.

My programmer is a Siemens RWB9 and has these connections:

N
L
1 (HW)
2
3
4 (CH)

Number 2 is not wired up.

 

[wilro15]

So I followed the instructions posted by D_Hailsham for testing the CH by wiring it up to permanent live and the valve did nothing. So this means Switch S1 is not working.

How is this resolved?

 

[wilro15]

Ok more weirdness...

The valve is still wired up to permanently on as suggested above. If I turn OFF the power I can hear the valve reset to neutral HW only position.

If I then turn ON the power, switch on the CH on the programmer and push down the valve lever FAST the system comes on! Hallelujah?

NO . . . the system comes on for about 2 seconds. Then I can feel something inside the valve "click" off, the valve lever moves up a bit and the system goes off.

 

[Crezzer]

Thats because by pushing the lever fast your springing past the micro switch momentarily which makes the boiler fire.

 

[wilro15]

Oh so nothing to get excited about then.

So I've diagnosed that Switch S1 doesn't work - does this mean the whole valve needs to be replaced?

 

[D_Hailsham]

The valve is still wired up to permanently on as suggested above. If I turn OFF the power I can hear the valve reset to neutral HW only position.

That's correct; the valve will reset to HW position.

If I then turn ON the power, switch on the CH on the programmer and push down the valve lever FAST the system comes on! Hallelujah?

But if the valve is still wired with white to a permanent live, the programmer is bypassed. So switching CH ON does not do anything.

Check that the valve is not sticking (see instructions).

If that does not resolve the problem, carry out all the tests, in the order given, and post results.

 

[Crezzer]

You can change just the head on certain valves, depends on how old it is.

 

[Space cat]

Maybe I'm missing something here but I've just looked up the data for the RWB9 programmer and pin 1 is No-HW. Pin 3 is the HW demand output - so why isn't it wired up to anything?

 

[matt1e]

the valve inserts a large resistance in series with the CH demand. This reduces the motor current to a low value; enough to stop the spring from driving it back but not enough to carry on forward.
.

not quite mate.
the valve switches in a diode in series with the resister which imposes a DC wave form on the motor which in turn stalls it

Matt

 

[Space cat]

the valve switches in a diode in series with the resister which imposes a DC wave form on the motor which in turn stalls it

Of course! Why didn't I spot that?