No hot water - 2-port valve opening but boiler not called

mwebst16 · 28 Apr 2010

Brethren,

Now that the weather is warmer and the central heating is no longer activating the boiler I have lost my hot water.

The thermostat on the hot water cylinder clicks if I turn it right down so I assume that is working, the timer on the programmer is active for hot water, in fact the 2-port motorised valve is definitely opening because if I force on the central heating then I eventually get hot water. That's not ideal though in this warm weather!

The only thing missing that I can determine is that the central programmer does not request the boiler to fire up.

I'm not experienced in the wiring output layout from the central programmer but I know my way round a multimeter so can do some pin-out checks if necessary if advised. The programmer is a Honeywell, details of which are at home. It has a separate twice/once/continuous/off option for heating and hot water. I tried resetting the programmer with the pinhole switch but this hasn't fixed the problem.

Any suggestions?

thanks

stem · 28 Apr 2010

Probably the microswitch in the hot water 2 port valve. The microswitch operates when the valve is open and turns on the pump and boiler, except in your case it isn't.

When the central heating operates, that valve turns on the pump and boiler and so if the hot water valve is already open that comes on too.

If you are competent to check with a multimeter (with the central heating set 'off' and the hot water 'on') the grey and orange wires to the hot water motorised valves should both be live. If one is live and one isn't the microswitch isn't working. A new valve head should fix it.

twgas · 28 Apr 2010

With the info you've given I'd be looking at the hot water valve not making the end switch - if that's the case a new actuator will solve it, if the valve spindle is seized then a complete valve would be reqd.

mwebst16 · 28 Apr 2010

OK guys, that's great info and I will investigate tonight.

So does the 2-port valve have 4 wires then? A live and neutral on the valve itself commanded from the programmer plus 2 wires on the micro-switch?

Not having explored one internally before I thought the programmer would send the command to the boiler/pump and a separate command to the valve but I suppose this is the way things are!!

stem · 28 Apr 2010

Yes and possibly an earth too.

Click here for a schematic of your system when calling for hot water.

mwebst16 · 28 Apr 2010

stem said:
Yes and possibly an earth too.

Click here for a schematic of your system when calling for hot water.

Nice one!

Thinking one step ahead - can the actuator be replaced without draining down the system? It's a pressurised system so even if I isolated before the 2-port valve I can see that getting complicated/wet.

stem · 28 Apr 2010

Most valves have a changable powerhead, so you wouldn't have to drain.

If it's a Honeywell, there's a bump on the lid at the opposite side to where the cable comes in that indicates it is one that can be changed.

mwebst16 · 29 Apr 2010

I can report it is indeed a Honeywell valve and also it is the microswitch that has failed. There is a potential difference of 240 V across this switch regardless of position of valve. The motor works ok.

Replacement actuator head it is.

thanks for the help

45yearsagasman · 29 Apr 2010

Depending on make can have 4 or 5 wires,the 5th being earth.
Neutral
Live to power synchron motor on call for heat.
Permanent live to micro switch
Live feed(usually orange) to power boiler.pump etc
Earth if applicable.
This is for power open/spring return valves.
Motor open,motor close valves are slightly different.

45yearsagasman · 29 Apr 2010

Sorry a bit late with that.Good luck

mwebst16 · 30 Apr 2010

thanks gasman, this ties in with a) the wiring diagram I now have and b) my own study of the existing wiring arrangement.

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No hot water - 2-port valve opening but boiler not called

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