CH Not Working - Suspect Mid-Position Valve

[fouxdafafa]

Hi, Turned on the CH today but the boiler didn't fire. Thermostat is OK I think, because it clicked "on". I'm suspicious of the ACL mid-position valve 679H340-30L0 - could it prevent the boiler from firing? I can sort of force hot water into the heating circuit by turning on the HW as well, and forcing the lever on the valve to the right. As soon as I turn the HW off the boiler goes off. I don't know that this valve has ever worked 100% since we bought our house. One thing I found odd was that if I put the CH on on its own, as well as the rads getting hot, the HW would also get warm. Now I'm thinking that it's developed other problems as well. How would I prove that this is my problem. I have a feeling the valve is quite old - probably over 10 years old. Thanks for any help.

 

[seco services]

This valve has a position indicator on the side.
W M H.
put the ch on only hw off the indicator should move to H.
If the indicator stays in position W then i would suspect the motor in the actuator has failed.

Ch on only you should have 230v on the
White wire from room stat
Grey wire from hw off on programmer
Orange sw/l to boiler

 

[fouxdafafa]

Ta very much for that. Just had a quick look, and when I turn the CH on the indicator stays in the W position and nothing happens at the boiler. So that points to the motor, yes? Haven't checked any voltages yet, will need to leave that til tomorrow. Would I need to take the cover off the valve? Never done that, but I can feel a screw at the back - is that the way in? Thanks again.

 

[seco services]

That screw is to remove the top cover it clips in the other end.
That'll gain you access to the motor etc.

To check the voltages follow the cable that should take you to a juncton box where all the cables meet and can be checked there.

 

[fouxdafafa]

A quick update on the problem. I still haven't had a chance to check the voltages, but a weird thing happened last night. As I mentioned previously I'd set the CH (only) on with the room stat high (30deg) and nothing happened. The indicator on the valve was still on the W setting. I then forgot that the CH was "on". At around 11pm, after I'd gone to bed, suddenly the pump started up - there's always a bit of gurgling so it was obvious. I didn't want to investigate further at that time so just switched the CH off. There's no programme that would cause the CH to start at such a time. Any ideas? Dodgy contacts in the valve electrics - dodgy microwsitch, that kind of thing? I'll get my voltmeter later.

 

[seco services]

What did you set the programmer to timed or constant ?
poss a loose connection in the junction box.

need to know if your getting 230v on the white wire when this happens.

 

[fouxdafafa]

White wire from room stat definitely reading 230. Checked by turning stat off and back on. Had to check it in the junction box because I can't see where to check at in the valve. I've taken the cover off the valve but it's very crammed in there - the motor prevents you getting to the wiring.

Forgot to say - CH is on constant.

 

[seco services]

You got a fault in the valve actuator.
could be on the pcb.

Fit a new actuator.

 

[fouxdafafa]

OK. Now, the silver thing with the orange wires that you included a picture of above, that's just the motor, yes? The actuator is the whole thing, yes? Like this

http://www.screwfix.com/p/drayton-mid-position-valve-actuator/40818

Not sure if I can just replace the actuator. Did I read somewhere that the older style can't be replaced, you have to replace the valve as well? If so, how do I tell whether I have old style or new style.

Thanks very much for your help with this.

 

[seco services]

Thats the actuator. But you can get them cheaper than that.

On the actuator where the W M H indicator is on the oppersite side is a black button the you can push in and lift the actuator off the valve.
You can see it in this pic.

 

[fouxdafafa]

Just checked - I'm afraid there's no button on mine. It must be an older version that's not "snap on". I suspect this means I'd need to replace the valve as well.

What about just replacing the motor?

 

[MANDATE]

You may like to do a search for author 'gooseander' and also 'grindstone'.
both had mid position valve problems with 679H340-3OLO and found the head is not interchangeable.

 

[fouxdafafa]

Confirmed it doesn't have a button on the side. Couldn't find a user called 'gooseander'. [EDIT - found him/her, there's no e in the middle - it's goosander]

Now, I'm wondering whether it's worth a go just replacing the motor. For the sake of less than £20, I would think it's worth a punt, because the alternative, unless I'm mistaken, is to replace the valve and actuator for one of the new varieties. I'd have to get someone in to do that, and I can't imagine there'd be any change from a two or three hundred quid.

I don't know if anyone on here has done this, but what I'd like to know is if I somehow mess it up would it still work for HW only without a motor. I'm wondering this because the valve is "stuck" at the W position, which I think is its default position. What I don't want to do is find that I've messed it up and leave our house without hot water until I can get a plumber to replace the valve. Could always use the immersion heater as a fallback though I suppose.

Any advice appreciated.

 

[seco services]

Check the old motor first before rushing out to buy one.
Remove the motor and put 230v through it.
Or check it for resistance should be around 2400 ohms.

 

[fouxdafafa]

Cheers for that. I'll probably leave for the weekend when I have more time. In the meantime I need to find where to isolate the power from the actuator. There's the fusbox, an isolating switch in the airing cupboard next to the junction box (but that could just be for the immersion heater), and maybe also a switch at the programmer. So many possibilities. Are there any permanently live connections to the actuator?