Vaillant ECOtec plus - no hot water unless CH on....help!

[moppit]

Hi Folks,
Wondered if you could give me list of possible causes before I pay for a call-out? Is this anything obvious/daft? Is there anything I could check (obviously non gas related!) from a DIY perspective?

System is open vented, with a hot water tank upstairs of unknown age. The boiler is around 4 years old. What is odd is that I get hot water when the heating is on but nothing on 'hw' only. The boiler fires up momentarily, gets to about 40 degrees and goes off. I've changed the tank stat just in case as it was a 5 min job but no change. Moving the boiler HW temp knob up to max does not do anything. Moving the CH knob up to max means the boiler comes on and off all the time at weird times(ie. no demand from controller as CH off) but I get hot water.

Very strange. Any thoughts?

Cheers

 

[gigz]

First check would be mid/three way valve, does it open for hw ? Or does it have two 2 ports ?

 

[moppit]

Thanks for the reply,

There is a drayton valve up near the HW tank, I'll have a look tonite and see if I can figure out what it is. I assume there is not a valve in the boiler too?

Thanks

 

[moppit]

So I could remove the actuator and check to see if it moves on/off as I switch the tank stat? To get hot water on a temporary basis I could switch the valve manually (CH not on at the moment obviously)

 

[moppit]

There are two Drayton ZA5 two ports. I slid open the manual release on the side and the pump fired up. In addition I turned up the control on the boiler with the picture of the raditor on it to 3/4 and boiler fired up and stayed on...I did not realise that the dial with the hot tap does nothing!

Looks like maybe an actuator playing up, will have a further play tonite as did not have much time last night.

Thanks

 

[St0rmer66]

Sounds like it could just be the Synchron Motor in the actuator to me. Either that or the valve sticking.