potterton suprima

[paulmatty]

I have the same tripping out problem as many on this board, however I have tested the voltage between the Neutral and SWL terminals in the boiler and get no voltage when the room thermo and programmer should be asking for heat.
If I bypass the controllers in the system and put a wire from the Live terminal to the SWL terminal in the boiler the boiler fires up OK. I then removed this wire to carry out the test below.
If I remove the programmer and place a wire between the Live terminal and the CH ON terminal and the room thermo is set at its highest setting (30), I get no voltage measured at the SWL terminal at the boiler.
The strange thing with the wiring in the room thermo is that when the room temp' is below the setting of the thermostat (ie calling for heat) the switched wire has no voltage but one of the other terminals in the room thermo which has no wire connected to it has a 240 v output. It has worked fine like this for 4 years. No one has rewired the room thermostat.
If it was the PCB as indicated on this board then surely I would not be able to get the boiler to fire up when I shorted the N and SWL terminals.
Or perhaps my understanding of how these things work is not as good as I thought!!
Any help would be gratefully accepted.

 

[breezer]

if it used to work, sounds like faulty stat, if it never worked (you said it has) i would say stat wired wrong0

it has to be either stst or wiring (unlikely) since when linking out stat boiler works

 

[paulmatty]

Thanks for your reply. I think I have narrowed it down to the 3 way diverter valve. The HW side of the system is working fine after a bit of investigation. However the CH side is the problem. The switched live from the room thermostat goes to the 3 way diverter valve (why) and when this SW live is triggered it does not give a constant SW live to the boiler. It gives a short (5 secs) signal to the boiler, the boiler then lights up but because the SW live signal stops after about 5 secs the boiler switches off again. The SW live is on constantly with the HW side of the system hence the reason why the boiler fires up and stays lit until the cylinder thermo or timer stops the SW live signal thus turning the boiler off.
This sounds to me like the 3 way valve is knackered but why does the SW Live from the Room Thermo go to and into the 3 way valve. It is OK when it goes in but as it comes out and goes to the boiler this is when the problem is.