Baxi solo 2 intermittent fault

[Aman]

Looks an interesting Forum, hopefully someone might give me some pointers before I have to call in an Engineer.

My boiler is a Baxi Solo 2 50 pf GC and was installed about 10 years ago.
No problems until recently for which I should be grateful!

The boiler fires up as normal and carries on through it's sequence all during it programmed times.
Recently it has been going into 'overheat' and on resetting, it works normally, cycling on and off.
The overheat happens occasionally(becoming more frequent, like 3 times in the last week) but only when the programmer shuts down.

I've tried simulating the fault by switching off the programmer manually but never getting this overheat problem.
The pump runs on then shuts down, however after about 5 minutes the pump relay clicks on and off maybe about 12 times, not a 'chatter' and the pump runs on and off until finally going off.
The regularity of the relay clicking in at this point could best be described as about the same rate as the sound of car indicators, but gradually the interval betwen clicks gets longer and finally stops

Any suggestions would be most appreciated.

 

[Agile]

It sounds as if the PCB is faulty.

Thats quite a common fault and I last changed one last Monday.

However, I always check the sensors etc. before changing any PCB.

Tony

 

[Aman]

Thanks for your quick response, I'll have another look later, just trying to avoid a larger bill than necessary!

As it happens I called home earlier and it was working fine and hadn't gone to overheat on the last programme, like taking a visit to the dentist, the fault has gone, but for how long!!

I can only see one sensor apart from the overheat stat on the pipe, so I might just change that before laying out for a pcb.

Thanks again, if I get a success I'll come back and let you know(no matter how long it takes

 

[gas4you]

I had this recently and ended up changing the pump, through another fault, this cured the intermittent overheat problem as well.

 

[Aman]

Thanks people.

The plot thickens, rather like my brain at times!!

I changed the sensor, whch didn't cure the problem then changed the overheat thermostat (just in case).
Took the plunge and changed the PCB, was fortunate to get a good price from a company called Trading depot.

Initially the problem appeared to go away, however when I set it for HW only it immediately went into overheat.
Seems the hot water is the root cause as the boiler can run through its cycle all day and night with both heating and hot water.

Tried venting the system to see if there was air but got nothing but water out, except, when on how water only it got like steam within minutes!

Air lock? but where? Pump appears to be running ok as everything works when both HW and CH are called for!

 

[Agile]

It sounds as if the circulation may be too slow.

Its not possible to know if the pump is working properly from the outside!

Can you measure the temperature differential across the boiler in CH, HW and CH+HW ??? That will give an insight into the circulation.

Tony

 

[Aman]

Thanks Tony,

I'll check that in the next couple of days. Fortunately, or otherwise, we still need the heating so I can keep HW and CH running ok in the meantime.

Again, thanks for the reply

 

[baxpoti]

This is far more likely to be a bypass/system problem