baxi combi 80. hot water - ok. ch- nothing

[freezingfergus]

Hello all,

hoping you can help. My system is Baxi Combi 80. controlled via timer Lifestyle LP711 and room thermostat Honneywell T6360B 1028.

There have been no recent faults with the system. Today, CH did not come on when called by timer and room stat. No fault lights on boiler, pressure is in range. DHW works fine.

I switched the power off and waited 5 minutes, then switched power back on and held reset position on boiler. Same issue, no heating but plenty of hot water. I believe the thermostat is working but absolutely no indication at the boiler. Any one help??

 

[easyflow]

Disconnect the room stat from the boiler and see if this works.
If not, probable cause will be damaged diaphragm/blocked sensing pipe or micro switch fault.

 

[freezingfergus]

Thanks for getting back.

When you say disconnect stat... There are 4 wires to my stat.

red to term 1 live
blue to term 2 neutral
yellow to term 3
earth to earth term

should I simply disconnect everything or bridge red to blue

 

[denso13]

Just connect red and yellow, working safely.

 

[freezingfergus]

power off. connected red to yellow. Power back on, timer to constant, not a titter at the boiler. DHW still works fine. Power off, re-connected stat. Power back on.

 

[JBPHS]

Disconnect the room stat from the boiler and see if this works.
If not, probable cause will be damaged diaphragm/blocked sensing pipe or micro switch fault.

Surely the hot water would not work either if this was the case?

Sounds like a controls problem (exterior to boiler). Most likely be the programmer.

James.

 

[freezingfergus]

Thanks Denso,

Hi JB, how would I go about proving the programmer/timer. I think we have proved the room stat.

 

[JBPHS]

Again working safely, remove the programmer so it reveals the backplate and wiring. Remove the wire from connection no 3 and connect into no 1. Test Heating function using the room stat. This links out the programmer.

James

 

[freezingfergus]

Thanks for trying James,

completed your suggested actions and got exactly the same result I'm afraid.

Still getting DHW but no CH. Still no fault lights on boiler but it refuses to do anything at all when heat is called for.

So that's the room stat and the programmer checked ok.

What would you suggest next.

Tony

 

[JBPHS]

Have you tested for ~230vac across terminal 3 and Earth in the room stat with it turned up and the programmer calling for heat?

Do not try this if you can't test properly or are not confident with testing live electrical equipment!

Failing that, looks like you may need a heating engineer as some components inside the boiler need testing. As I'm assuming you may not be Gas Safe Registered, you will not be able to test the safe operation of your gas appliance once you've finished working on it?

James

 

[freezingfergus]

Hi James,

I'm not sure about testing across live (term1) and earth.

I did a continuity check from earth to all terminals with the power off and there was no circuit on any.

Just checked the following with power on and programmer calling for heat:

Stat turned down to off
live on 1 to neutral on 2 shows 65ish volts
live on 1 to Timer? on 3 shows 50 volts

Stat turned up (To call for heat)
Live on 1 to neutral on 2 shows 230v
Live on 1 to Timer? on 3 shows zero v

using simple multimeter. correct, I am not gas safe.

Tony

 

[JBPHS]

Assuming it's wired correctly it looks like your controls could be ok. It now looks like the problem lies between the room stat and the boiler (inc the boiler itself).

You do need a heating engineer to investigate further.

James.

 

[ianmcd]

go to your boilers wiring terminals and note the position of any wires connected between terminals marked 1 + 2 remove these wires and place a temp link between the terminals 1 + 2 and if the boiler now fires then it is indeed an external control fault if not then it is a boiler fault

 

[freezingfergus]

Well, I guess that confirms the fault is in the boiler. With terminals marked 1 and 2 linked and external controls isolated, the boiler still refuses to give me heat.

My thanks to all of you:
easyflow, denso13, james of jbphs and Ian of ianmcd

Wishing you all the very best for 2014
Tony still freezingfergus.

 

[JBPHS]

Sorry we couldn't help you much more.

All the best for the New Year!