NO hot water after replacing Motorised valve

[Walkbar]

I've replaced my Drayton TA/M4 valve with a Honeywell 4073A and completely rewired the system to a Y plan (Yes! you do have to) thanks to some advice from you lads.
My problem now is that everything seems to be doing what it should as per the controls, when the valve switches to hot water only the top of the heating coil gets hot and the bottom remains cold.
The top then seems to cool down shortly after.........I think this because the boiler cuts itself off.
Heating seems fine ....Rads up and down hot when they should be.
It seems water not flowing through the heating coil but it has one of those bleed caps and I've been bleeding it (little bit of air each time)
What now?

Boiler is Ideal Standard WRS

 

[ChrisR]

If you have yer orange wire turning the boiler on, and either that or the boiler itsefl turning the pump on, I don't see anything obvious. Is the pump on when the HW is on? If it were not, the boiler would heat up & turn off quickly, which it sounds like it could be ??

I would be interested to now what this turns out to be.

 

[Walkbar]

I would be interested to now what this turns out to be

Thanks for the advice , everybody.
When my plumber replaced the valve, the pipes were in the normal "T" config. and he fitted the Honeywell likewise but didn't notice that the old Drayton TA/M4 has the AB port on the SIDE, so that when the system called for Hot Water only It closed the AB port, hence the problem...The AB port and heating were reversed...He's been back and rectified it.
NEW PROBLEM; I cant get the downstairs rads to heat up (pump is working).
Flow pipe to downstairs hot......Return pipe cold.
I had the same problem when I refilled after the first valve change.....got round it by filling backwards from the drain cock.....Waddya think.. fill it via the flow drain cock or the return drain cock.
My boiler Ideal Standard WRS has the pump in the boiler cabinet and it looks to me like it pumps straight in to the lower boiler tapping first , surely this means it's on the return side of the boiler....it's been working like this for 25 years!!!

 

[ChrisR]

Lots of systems have the pump on the return - including mine. Lack of circulation is likely to be lack of water, an air lock, or sludge.

 

[Walkbar]

Lots of systems have the pump on the return - including mine. Lack of circulation is likely to be lack of water, an air lock, or sludge.

Thanks for the help.
Air lock seemed to be the problem.
Reverse filled the system and whilst it was drained, checked and replaced the downstairs TRV's ......All OK now.
Suspect replacing the TRV's solved the problem and I could have refilled normally but I'm not about to refill normally just to find out!!!!!!!!!
Thanks again