Baxi 105e - DHW but no CH

[electronman]

Hi There,

My boiler has started playing up, in that the boiler fires up fine when there is a demand for DHW but nothing when demand for CH.

I have checked the timer, and even bypassed this for troubleshooting purposes by connecting terminals 1 and 2 together on the boiler terminal block, as they were before the timer was fitted. Still no CH.

I have also swapped CH and DHW temp sensors and DHW still works but CH doesn't. I have checked safety stat on CH flow pipe and this has continuity, so I assume this is ok.

When the timer is on the boiler doesn't do anything, i.e. the CH green neon doesn't light and the boiler doesn't fire up.

There is no Room stat currently fitted, although I do intend to fit one of these soon. Therefore, I can eliminate that as the cause of the problem.

Does this sound like a duff PCB to you?? Any ideas of what else to check?

Any help would be most appreciated.

+++++++++++++++++++++++++++++++++++++++++++++++
I should also point out that there are no flashing neons on the front panel, which I understand would usually flash to indicate a fault.

Thanks,
electronman.

 

[baxpoti]

Any ideas of what else to check?

The primary flow switch

Try increasing system pressure half a bar as a temp fix

 

[electronman]

Hi Baxpoti,

System pressure is currently at 1 bar. Where is the primary flow switch located?

Thanks.

 

[electronman]

I have just spoken to Partcenter and they have a PCB in stock, so I'm tempted to replace it anyway.

Incidentally, I've just taken one of the 12V relays off the PCB to test and when energised, the contacts don't appear to be making properly, i.e sometimes the resistance is 0 ohms, sometimes it's 11 ohms, other times it's nearly 100 ohms. Could this be causing the heating to fail to start up?

I'm not sure what this particular relay operates, but the resistance readings certainly don't look good to me.

 

[electronman]

Are you referring to the Primary valve spindle that makes with the microswitch when you mention 'primary flow switch'?

I have observed that when there is a demand for DHW, i.e. sink tap turned on, both spidles on the Diverter valve assembly protrude and make with their respective microswitches, and then both retract when the tap is turned off. Is this how they 'should' operate?

I noticed last night that the CH came on again for a short while but then stopped working! Does this provide any clues to the possible cause?

 

[baxpoti]

Are you referring to the Primary valve spindle that makes with the microswitch when you mention 'primary flow switch'?

Yes

I have observed that when there is a demand for DHW, i.e. sink tap turned on, both spidles on the Diverter valve assembly protrude and make with their respective microswitches, and then both retract when the tap is turned off. Is this how they 'should' operate?

Yes

On C/H only the top one should operate (or not in your case)

Check this b4 new pcb

 

[electronman]

Hi Baxpoti,

So, should the front spindle (only) operate when demand for DHW, and the spindle on the top (only) operate for CH?

They are both definately activating the their respective microswitches when demand for DHW, but neither are activating when CH should be on. Does this mean that the diverter valve is faulty? Both spindles retract when sink tap turned off.

The DHW is working fine and reaching a nice temperature.

Any ideas??

I am reluctant to replace pcb unless I know it is definately the cause of the problem.

Could I disconnect one of the wires from the DHW microswitch and then manually activate the CH microswitch to see if the heating then kicks in?

 

[Agile]

Incidentally, I've just taken one of the 12V relays off the PCB to test and when energised, the contacts don't appear to be making properly, i.e sometimes the resistance is 0 ohms, sometimes it's 11 ohms, other times it's nearly 100 ohms. Could this be causing the heating to fail to start up?

This is amazing taking relays off the PCB! Rather risky I would have thought too!

If you can do that the surely you can trace which external device is powered from the relay contacts?

In any case I thought the relays would have been 24v coils?

Its much more likely to be a simple flow switch problem.

You keep on talking about the boiler "not firing up"!

To diagnose the problem you have to start at the beginning. Does it respond to a demand for CH by starting the pump???

Tony

 

[baxpoti]

Could I disconnect one of the wires from the DHW microswitch and then manually activate the CH microswitch to see if the heating then kicks in?

Forget hot water
Just manually lift the primary flow microswitch, if the pumps running you'll get hot water down the C/H flow pipe

 

[electronman]

Hi Baxpoti,

I tried lifting the primary flow switch manually and nothing happens at all, i.e. the pump doesn't run and the boiler doesn't start up. I suppose I could check continuity of the microswitch.

Any other ideas as to the most likely culprit?

 

[electronman]

Tony, I think the new boards use 24V relays, but mine, which is an older issue, uses a combo of 12 and 24V ones.

I'm still trying to work out why both spindles come out when there is a demand for DHW. Is this correct?

If the front spindle (DHW) demand switch is closed, then would it still work if I then closed the CH switch manually? That's why I wondered about removing the wires from the DHW microswitch to take this out of the equation altogether.

Thanks.

 

[baxpoti]

Im still trying to work out why both spindles come out when there is a demand for DHW. Is this correct?

Yes


Link out your built-in timer, short out the black wires behind the clock

 

[electronman]

Hi Baxpoti,

Tried that already, as per my original post, in order to elimate the timer as being the problem.

Does the pump not running up suggest something electrical to you, i.e. the PCB, microswitch or a sensor?

I can purchase a new PCB and fit it today if necessary, but want to rule other things out first.

Thanks,

 

[baxpoti]

I tried lifting the primary flow switch manually

you mean the microswitch on the primary flow switch?

The one with red wires going to it?

 

[electronman]

Yes, that one.