Hi all,

Hot water is working OK and the roomstat clicks when dial turned, but the boiler doesn't fire up for central heating!

1) Can anyone tell me how to test my roomstat, can I short it out to bypass it?

I pulled the cover off the roomstat and found 4 wires
Red, Yellow, Green/Yellow, all connected (plus a blue which was not conected to anything)

Although the blue was disconected the screw connection was reasonably tight making me wonder if it's not required.

2) Should the blue wire be connected?

Anything else I can do to diagnose the problem

Thanks for your help

The blue one is netraul, and shoule be connected

The room stat switches red & yellow, so you could try linking these out.

Ensure you turn off the fused spur first.

Its most likely to be the syncron motor in the motorised valve, to confirm this you need to test live voltage to it.

===========================
Ah, I've had trouble with the valve motor for some time now. The (3-way)valve has opened the heating valve when the water comes on. I put thermastats on the radiators so I wasn't too bothered about this.

Are you saying that the motor has now packed up completely and this stops the boiler from coming on?

Many thanks for your reply

Hiya,

Thanks for your help so far.

I connected the blue wire on the stat.
It's really strange that it was disconnected. The heating and stat were both working OK last weekend. The wires and stat aren't in a place where you might expect the unit to get a bump and make a bad connection. The screw to connect the blue wire seemed tight without the wire inserted.

Same problem: Boiler doesn't start when stat dial turned up

I've just fitted a new Syncro motor.
Same problem: Boiler doesn't start when stat dial turned up

Any more ideas?

does the heating get hot, with the hw turned on?

Did you try linking the red & yellow wires together on the roomstat?

Really to find fault it needs testing with meter. the voltage at room stat & on the white or brown wire to 3 port valve needs testing.

The valve may be suspect if you say was passing to CH with the hot water on, if it doesn't have full travel, then it wont move across futher enough to activate microswitch.

"does the heating get hot, with the hw turned on?"
Yes it does

"Did you try linking the red & yellow wires together on the roomstat?"
Yes, I've just done that and have the same problem that the bioler is not starting up for the central heating (but it does for the HW)

"Really to find fault it needs testing with meter. the voltage at room stat & on the white or brown wire to 3 port valve needs testing. "

I'm happy to try this but need further clarification which wires to connect to meter for each test.
This is what I've got
Stat Motor Motor PCB Prog Pump Boiler
RE BL

YW WH WH

BL OR BL BK BK

GN/YW Earth

It's not the valve not working which allows HW to seep through to rads when the HW comes that's casuing me grief. I'd like to resolve this issue but it's the fact that the boiler doesn't ignite (activate) when I turn on the Heating (by shorting red/yellow or turning dial up) that's making me chilly.
When I turn the stat up on the cylinder it activates the boiler (I can hear it and test temp of pipes). When I turn the heating on the boiler doesn't ignite.

Would the motor or valve being faulty stop the boiler from starting up?

Please let me know which wires to atach meter to and I'll post results

Many thanks for your help

The formatting was lost when I posted the wiring description so I've atached a file which hopefully explains a little better

I tried reading the AC Voltage between red/Yellow wire and the Blue wire on the stat and got nothing. I wasn't expecting that?

Just measured the voltage between
red (stat) and Blue (Motor PCB) 232V
Yellow (stat) and Blue (Motor PCB) 232V

Felt the motor - VERY HOT INDEED

The ULTRA MIN SW C/O PCB MOUNT FK4T8 on the Motor PCB appears to have burned out

Just popping down to Maplins to see if I can get one

Once again I wouldn't expect this to stop the boiler from coming on if the thermostat was turned up. I wopuld expect the boiler and pump to come on but maybe not get passed the valve? Can anyone confirm?

That shows the clock and the room stat are both ok

Have you tested voltage to the syncron motor?

do you have 232v between the two wires?

the wires in to the valve are as follows

Grn/Yel Earth

Blue Neutral

Grey Hw off - voltage sent by either clock hw off circuit, or the cylinder stat off terminal

White/brown CH on - voltage from yellow wire on room stat

Orange Power to pump & boiler -
(a) gets power from either the HW on from cylinder stat (hw req or hw & ch req) :
(b) gets power from microswitch in 3port valve, when valve moved fully across to CH (ch only selected)

I'm thinking you'd be better off to change the whole valve, as i think either the ball inside has expanded, or the spindle is stiff, prevent full movement to activate microswirch when in CH only mode, and the CH port closing off, when in hw only mode.

What make of valve is it?

The valve motor box says it's a landis & staefa part number mav-322

ok, just wondered if a honeywell one.

Providing you have power on the brown (or white) CH on wire... then I'd change the complete valve.

I'd recommend a ACL 3 port valve.
http://www.inspiredheating.co.uk/cgi-bi ... 3_2f302101

The wiring will be the same, and the plumbing isn't any harder than when you fitted the TRVs.

This will fix both problems.

Do you happen to know where i could get hold of one today?
I'm off to London early tomorrow morning for the week and I don't want ot leave the children with no heating.

Thanks

Do you happen to know where i could get hold of one today?
I'm off to London early tomorrow morning for the week and I don't want ot leave the children with no heating.

Thanks