Baxi Genesis 80 not firing

[JohnFeeney]

Hi,
I have a Baxi Genesis 80. It has stopped working - it will not fire on either CH or DHW. The green power light is on, the pump runs and the fan runs (on hot water - haven't checked the fan on CH). An engineer attended and said the pressure switch needed changed - he changed it and no effect - still the same. He then said the PCB needed changed (I pointed out that there are 2 and he said best to replace both). Both have been changed but to no avail. I believe he is just guessing. When demand for hot water is asked the pump runs and the fan runs but no sparks at all. Could it be the spark generator or perhaps the overheat thermostat or the main on/off solenoid on the gas valve or the gas valve itself? does anyone have any idea?

Thanks

John

 

[bazdaman]

Tried linking out pump flw switch?

 

[Agile]

You should not have to pay for parts which are not required to repair the boiler.

He is someone with no diagnostic skills and is what we call a "parts changer".

How on earth did you find him?

I expect the fault is a smaller part which can probably be cleaned but to replace would only be about £34.

Tony

 

[JohnFeeney]

Hi,
I don't think there is a pump flow switch - there are separate ones on the CH and DHW - but it does not work on either so I don't think it is that. As far as the "engineer" is concerned I called Baxi and got some numbers close to me but they were all too busy to attend due to Xmas and one of them gave me his no.
Tony I have read some of your other posts and you clearly know what you are talking about. I'm an electronic engineer by trade so am going to do the continuity tests on the air pressure switch and check the overheat stat for continuity then the mains voltage to the spark generator - does this sound sensible - do you have any other advice. Do you know what voltage is applied to the solenoids (ac/dc / value)

Thanks

john

 

[bazdaman]

Link the ch flow switch out it also acts as a primary flow switch dont test anything inside the combustion box, the part tony refers to that can be cleaned out sound like the flow switch i mentioned, if that dosnt make when pump runs then nothing else will work

 

[JohnFeeney]

Thanks bazdaman I will try that. Tried that did not work. I notice fan not running on CH but running on DHW but still no spark. The pump runs on both

 

[Agile]

The pump proving switch has to be operated on both CH and DHW for the boiler to proceed to the ignition stage.

They are plastic shuttles which contain a magnet and when moved by the flow the magnetic field operates a reed switch.

Only slight design problem is the magnetic field attracts magnetic iron oxides in the system water and jams the switch!

The reed switches also have to have a high OFF resistance. I once saw one and whilst it made correctly the off resistance was about 30k and enough to keep it in DHW demand mode. That took me a few more minutes to identify as I measured the "on" resistance with a low range. But disconnecting at the plug removed the demand and identified the problem.

Tony

 

[JohnFeeney]

Thanks Tony for the reply.
When you say pump proving switch is this the CH flow switch that Bazdaman mentioned or is there another switch I have missed. I pulled the connector off the CH flow switch and shorted the connector (CH did nothing at this stage), turned the tap on and the fan and pump kicked in but still no spark. I checked the air pressure switch - before DHW c/nc short, after DHW c/nc short and c/no short - I believe this is how it should be. The faultfinding flow chart asks to measure a voltage on the power board when DHW which went from 0-24v when demand given. It then asks you to measure for mains voltage on the terminals supplying the spark generator - there is no voltage at all so spark generator not being supplied. It then tells you to change the control board - which has already been done - to no avail. I am now starting to pull my hair out.

John

 

[Agile]

With a demand for CH you can see the continuity on the pump proving ( flow ) switch if the pump is running.

But that same switch must be made to enable the ignition sequence to proceed on both CH and DHW.

Tony

 

[JohnFeeney]

"With a demand for CH you can see the continuity on the pump proving ( flow ) switch if the pump is running" - not sure which switch you mean here

John

 

[bazdaman]

Have the new pcbs been set up correctly? There are lots of dip switches on the pcbs and links.

 

[JohnFeeney]

Yes I double checked the switches on the control board - there are 2 either side of ribbon cable. All links are the same. Off the top of my head there is only one link on the power board - but it is the same also.

 

[picasso]

Bit of a long shot but on some baxis its possible to put the control knobs 180 out of position, so it looks like they are full up but they are actually switched off.

 

[jeff the gasman]

The old Genesis had 3 solenoids IIRC

 

[Agile]

Well the gas valve does but that's not the issue here and in any case we cannot discuss them.