Three port valve problems - please help?!

[BarryBodge]

Here's my problem, I started a 5 minute job on sunday to replace a room stat with a cracked dial - now i've got no heating and have run out of ideas.

I replaced a Honeywell T630B room stat with a Sunvic TLX 4101, and managed to blow the fuse in the circuit isolator twice in the process before getting it to work. Everything seemed fine but when the heating came on none of the radiators heated up. I subsequently put the old room stat back on to fix it - this didn't work.

I thought initially it was the pump as the water was heating up, no1 radiator on the loop was getting warm but nothing else. The boiler also seemed to cut out after about 10 mins of use.

Last night I found it wasn't the pump after using the manual override on my three port valve (Honeywell V4073A) and getting heat to all the radiators. Putting it back to auto gives me no heat again

I've tested the contacts on the three port valve with a multimeter and have 240V between orange and white and 105 between orange and grey when heating and water are on?? The 105 disappears when I turn the water off. The room stat appears to have no effect on the boiler firing whatsoever.

I can't figure out what i've broken, whether it's the three port valve, the room stat or the control box (Centaurplus C27).

Can anyone give me any ideas on isolating the problem please - my money's on the valve head but i'm not sure?

Many thanks...

 

[D_Hailsham]

The Honeywell Wiring Guide has step by step instructions on fault finding.[/url]

 

[MANDATE]

Putting it into manual over ride, means you have moved the quadrant and valve over half it's range. The valve is in its mid position and you get HW and CH.
So why did it not move to the mid position without using the lever?
Well it could be the motor in the actuator head that is faulty. Or the motor is not receiving power which comes from the 'room stat'
If the room stat is working it should make the 'white wire' leading to the valve live. (test white to neutral)It's power through the 'white' that drives the motor over the first half of the range.
The 'grey' and 'orange' play no part until mid point is reached.
If 'grey' is live when mid point is reached, then it takes over from where white left off and drives quadrant over last half of range.
When HW is in demand the cylinder stat is the power source for lighting the boiler, but if it's not on or is satisfied and only CH is involved then power has to come from elsewhere and that out from the 'orange' wire.

So does white come live or not? if not then it's back to wiring and room stat, or even programmer.