boiler does not run CH & HW together

[peterJohnB]

My heating and water boiler was replaced about 3 years ago and has been running fine until recently, when I am unable to run both at the same time. separately both work fine, if I switch on the HW then CH it will stay in the HW position, if I switch on CH then HW it will go to the CH position. I have followed your boiler FAQ No.17 where I have found that the 3 port valve moves freely and on the electrical test for hot water everything works as it should and central heating it also work fine. I then follow the instructions for CH and HW and the boiler does not come on. As suggested I replace the HW cylinder stat but the same problem occurred. I have now replaced the 3 port actuator. It seems to go straight to the CH position A port and nothing else happens . I would be grateful for any suggestions As I have said we are not stuck without CH or HW but cannot run both together

 

[jackthom]

Can you post a photo of the inside of the wiring centre and are you happy using a multimeter to measure some mains voltages ?

 

[dcawkwell]

It is wired wrong.
Rip it out get a picture of the 3 port wiring diagram and redo it.

 

[D_Hailsham]

My heating and water boiler was replaced about 3 years ago and has been running fine until recently, wheon the electrical test for hot water everything works as it should and central heating it also work fine. I then follow the instructions for CH and HW and the boiler does not come on.

Did you follow the instructions in the exact order given in the FAQ?

This is important as many tests assume you have done what comes before.

What was the programmer set to when you carried out the tests, e.g once, twice, or on?

 

[peterJohnB]

As I stated my system was functional until recently. I had not changed anything before it went wrong so wiring was still correct. Following advice and to rule out anything, I have disconnected everything, checked wire for wire unit by unit. I then ran the test again but still could not get past the HW and CH test. I removed the timer and shorted out Live, 3 and 4 terminals, HW on and CH on respectively. I switched the power on and hey presto it worked. This shows a timer fault so for others I replaced the timer, disconnected the wires at the terminal block leaving L and N connected, connected 1, 3, 4, to a separate terminal block and tested the voltages out
With no times set and all buttons showing off
Term 1 voltage reads 244
Term 3 voltage reads 45
Term 4 voltage reads 46
Press button once for HW
Term 1 voltage reads 25
Term 3 voltage reads 243
Term 4 voltage reads 37
Switch off HW and press button once for CH
Term 1 voltage reads 241
Term 3 voltage reads 58
Term 4 voltage reads 241
I press button once for CH and press button once for HW
Term 1 voltage reads 240
Term 3 voltage reads 57
Term 4 voltage reads 240
I reverse the last procedure and press button once for HW and press button once for CH
Term 1 voltage reads 25
Term 3 voltage reads 241
Term 4 voltage reads 38
The last 2 test should show 240 volts on 3 and 4 and this is why I was only able to get HW or CH separately and not together
Thank you for your replies

 

[D_Hailsham]

Is there a switch, or a jumper, on the back of the timer? If so, make sure it is in the P (pumped) position.

 

[peterJohnB]

Yes it has a switch and it is set for pumped thank you

 

[D_Hailsham]

Thanks for confirming that the switch is set to P.

You haven't said which timer you have.