Problem with Baxi 105he

[dan_the_plumber]

Hello all.

I’ve got a problem with 105he driving me mad.
When you switch boiler on and set heating demand the pump starts for 1-2 seconds then clicks out, then starts again, then clicks out again, then starts again, over and over again.
I’ve done whole lot of electrical tests. I phoned Baxi and they told me it wS the PCB at fault. I agreed with this so replaced the PCB and guess what...The same fault.
I wondered if anyone could tell me what the fault might be please?

Dan

 

[townfanjon]

After the pump has stopped is there voltage to it

 

[AMGasServices]

Have you changed the thermistors ?

 

[dan_the_plumber]

After the pump has stopped is there voltage to it

No voltage flicking on and off

 

[dan_the_plumber]

Have you changed the thermistors ?

No I haven’t changed thermistors. But wouldn’t pump at least run? I thought voltage from thermistors comes later in the lighting sequence?

 

[dan_the_plumber]

I’ve alteady checked continuity through high limit stats. Also on hot water demand, nothing happens at all, the pump doesn’t even start at all.

 

[AMGasServices]

The only reason I say that is because I had a similar fault on a 105. A few of my associates went to it but couldn’t find the issue I got an invitation to deal with it after checking the thermistors (just connecting them to the leads) the boiler sprung back in to life.

 

[AMGasServices]

From looking at the diagram have you tried to remove the flue overheat sensor below the sensor there is a nut. Remove the nut using your u gauge tube blow in to that hole. Any crap in there can cause a lot of issues.

At the same time check the flue overheat stat (try linking it out).

 

[Last Plumber]

Flow Switch.
Did you check that?
Pump starts, flow switch operates, start up sequence continues. If the switch doesn’t operate, nothing will follow.

 

[dan_the_plumber]

Flow Switch.
Did you check that?
Pump starts, flow switch operates, start up sequence continues. If the switch doesn’t operate, nothing will follow.

Glow switch opporates fine. But if I opoorate glow switch manually still nothing happens. I’ve already changed PCB

 

[Harvest Fields]

Glow switch opporates fine. But if I opoorate glow switch manually still nothing happens. I’ve already changed PCB

Where did you get board from? Any water damage to it?

 

[dan_the_plumber]

Where did you get board from? Any water damage to it?

Brand new board from city Plumbing spares. Looks pretty spot on to me.

 

[Harvest Fields]

Brand new board from city Plumbing spares. Looks pretty spot on to me.

Normally it is the board. Is the pump diff staying in position on the microswitch?

 

[dan_the_plumber]

From looking at the diagram have you tried to remove the flue overheat sensor below the sensor there is a nut. Remove the nut using your u gauge tube blow in to that hole. Any crap in there can cause a lot of issues.

At the same time check the flue overheat stat (try linking it out).

There is actually a fair bit of build up around that nut.
Passed a continuity test though. I might well try cleaning it out, see if that helps, Thanks

 

[Harvest Fields]

There is actually a fair bit of build up around that nut.
Passed a continuity test though. I might well try cleaning it out, see if that helps, Thanks

For the price of it. I would take a diaphragm as well.

 

[AMGasServices]

There is actually a fair bit of build up around that nut.
Passed a continuity test though. I might well try cleaning it out, see if that helps, Thanks

Did you try to link the overheat stat out ?

 

[dan_the_plumber]

Yes

Did you try to link the overheat stat out ?

I’ve done that already

 

[AMGasServices]

How you getting on with it ?

 

[dan_the_plumber]

How you getting on with it ?

Well actually I’m away on holiday atm. But I’ll try your suggestions out again next week...Thanks for your advise!