No hot water but heating on max instead

[steviewevie]

I have a conventional boiler (not combi) with separate hot water cylinder.

Today, for the third time in a couple of weeks, I've found that there is no hot water (with the hot water control being turned on, and the heating turned on too) after the hot water in the tank was used up. Plus the heating had gone crazy and was staying on (so the temperature where the room thermostat is was way above what the thermostat was set to).

Like the last couple of times, I've turned off the heating and hot water via the timer controls and turned them back on again, and I suspect this will (like before) reset the situation.

Any ideas as to the likely cause though? I was hoping it was a one-off, but it appears not to be. Thanks.

 

[ianmcd]

sounds like you have a faulty 3 port valve

 

[stem]

I agree with ianmcd. I think that you have a intermittent fault within the motorised valve.

There are two microswitches inside the motorised valve, if the first one (shown on the left in my diagram below) does not change over as the valve opens it would cause the situation where the valve remains in the heating only position, and the hot water cylinder thermostat will keep the boiler going. The drawing is shown in the fault position with the red line showing the fault circuit. in this position, the hot water port is closed off, so the hot water will not heat up but the heating will stay on regardless of the room thermostat being satisfied.

Turning off the hot water at the programmer will remove the live it was sending via the cylinder thermostat to the boiler which is being fed back to the valve motor via the orange wire and keeping the valve in the heating only position.

 

[steviewevie]

Thanks, both. So this is a valve that is part of the plumbing inside my airing cupboard with the hot water cylinder, the metal box attached to the plumbing, right? So it shouldn't be a terribly big job for someone to come along and replace the valve for me? Thanks.

 

[stem]

It will look something like the one in the photo below and can usually be found near the hot water cylinder. It will probably be necessary to drain down part of the system before removing it.

Untitled

• stem
• 1 Apr 2010
• 8

 

[HERTS P&D]

THIS ONE:

https://www.screwfix.com/p/honeywell-v4073a-3-port-motorised-valve-22mm/31421

Andy

 

[steviewevie]

Thanks, all. Does it matter what position that lever at the rear of the box is in? Because as I was moving stuff out of the way and "found" that switch by feel, I'm not sure if I've moved it into a different position or not.

 

[ianmcd]

post a pic of the one you have as there are different makes and some you can just change the head without draining anything , some you have to drain

 

[steviewevie]

It seems to be a Honeywell one that I have at the moment.

IMG_20180323_172836

• steviewevie
• 23 Mar 2018

 

[stem]

You can change the head on that one, the dimple on the top is the indication of that. However, if the top is old, the bottom would be too, so personally I would change the whole thing. But that's your choice. It's an easy DIY fix just to swap the powerhead over.

The lever should be in the 'auto' position the other position 'man' is there for filling the system only. However, the valve should automatically revert to the 'auto' position as it's used.