3 way valve not working correctly.

[Ches1andonly]

After changing the cylinder stat I now have a issue with the 3 way valve. It works fine apart from when the hot water has been the last thing on. When the heating is the next to call on its own it goes to mid way and just stays there. If you then turn the hot water off on the controller it continues to heating and the boiler then starts. Guessing its a wiring issue.
Recap
Heating only fine
Hw only fine
Heating and Hw fine
Hot water not calling but on heating calls valve moves from hw to mid position and just stays there.
Any ideas on wiring checks?

 

[Echo the husky]

Yes your hot water satisfied signal from your cly stat is not putting power to the grey wire of the valve to force it to move to heating only. Either loose wire or crossed wire. What stat did you fit? It should have 3 connections and possibly a 4th for earth.

 

[Ches1andonly]

Drayton HTS3 replacing a HTS2.
3 connections

 

[Echo the husky]

Common should be wired to HW on from the programmer
1 should be connected to the orange wire of the valve (which also connects to the boiler and pump)
2 should be connected to the grey wire of the valve (which also connects to HW off from the programmer)

 

[Ches1andonly]

Currently at work will check it out later and let you know.

 

[Ches1andonly]

Have wired the new stat correctly didnt touch anything in the junction box used existing wire to connect to cylinder stat.

 

[Echo the husky]

I'm guessing from your post it was wired correctly but still doesn't work?

If so do you have a multimeter and know how to use it safely? All measurements carried out with one lead from the meter connected to neutral.

If so when the cylinder is up to temperature and the heating is on as well at the valve wiring there should be:
240V present at the grey wire
240V present at the white wire
240V present at the orange wire

If you are getting a voltage substantially less than 240V at the grey wire then you need to check for voltage at the cylinder stat.
With the heating on and calling and,
hot water on at the programmer,
and the cylinder stat turned down so it is no longer calling for heat.
There should be 240V on all 3 terminals of the cylinder stat.

If there is, there is a poor connection between the cylinder stat and the wiring centre. Could be trapped insulation etc.

If there is a random voltage on terminal 2 of the cylinder stat that is much lower than the voltage on the common and 1 terminals, then the new stat is faulty and will need to be replaced.

If you switch the heating on and hot water off at the programmer, I take it the valve moves to heating only?
In this condition at the valve wiring there should also be:
240V present at the grey wire
240V present at the white wire
240V present at the orange wire

 

[Ches1andonly]

Ok I have never used a multi meter. One thing i have noticed is that if you turn the dial all the way down on the cyl stat it the heating starts. Looking at the instructions this represents off. So I guess its the same as turning the controller off but might mean the cyl stat is faulty.

 

[Ches1andonly]

Freddo your a absolute star!!!
Did what you said terminal 2 was giving a low voltage. Been and exchanged it for a new one. Its fitted and working perfectly.
Thanks very much for taking the time to help me on this its very much appreciated

 

[Echo the husky]

Glad you got it sorted!