Variable voltage to boiler from tank PCB: Boiler not firing

I have a Gledhill Systemate III connected to Maxol Microturbo 405/505 Gas boiler (no immersion or other input).

The problem I am currently experiencing is that when the system is switched to central heating the voltage from the tank to the boiler drops, and hence the fan stutters, the boiler won't fire and goes into fault mode. When on water heating or tank heating, the boiler runs, but intermittantly fails due to the same voltage issues.

I have had a couple of engineers out, and the following has been performed
- Replaced actuator on 3 port valve
- Replaced Systemate PCB (twice)
- Replaced Boiler fan

In the first instance, the boiler fan shorted which spiked back and wrecked the PCB, making the whole system electrically dead until a new fan and PCB were fitted. The system then ran perfectly for 5 days until the above fault regarding the central heating occurred. I have since had another engineer review the system for a second opinion, came to the conclusion that the replacement PCB was faulty, and fitted another PCB. This fixed the problem for another 48hrs, and now the fault is reoccurring.

Does anyone have any idea what might be causing this fault as replacement PCBs are not cheap or easy to come by!

I have tried the Gledhill tech support but can't seem to get anyone to answer the phone, and emails direct you to the phone line.

Hi c murray,

This seems like a loose connection to me. Not hard to trace the low voltage back from the boiler to it's source using a multimeter.

One thing puzzles me though. The MicorTurbo should have it's own permanent 240V supply and the Systemate just supplies the 240V 'call for heat' signal. Which of the two 240V connections into the boiler is low? What voltage IS the low one, exactly?

This problem is usually associated with a high resistance microswitch in the motorised valve actuator, but you say you've had this changed....


Cheers, Mike

c murray wrote:I have a Gledhill Systemate III connected to Maxol Microturbo 405/505 Gas boiler (no immersion or other input).

The problem I am currently experiencing is that when the system is switched to central heating the voltage from the tank to the boiler drops, and hence the fan stutters, the boiler won't fire and goes into fault mode. When on water heating or tank heating, the boiler runs, but intermittantly fails due to the same voltage issues.

I have had a couple of engineers out, and the following has been performed
- Replaced actuator on 3 port valve
- Replaced Systemate PCB (twice)
- Replaced Boiler fan

In the first instance, the boiler fan shorted which spiked back and wrecked the PCB, making the whole system electrically dead until a new fan and PCB were fitted. The system then ran perfectly for 5 days until the above fault regarding the central heating occurred. I have since had another engineer review the system for a second opinion, came to the conclusion that the replacement PCB was faulty, and fitted another PCB. This fixed the problem for another 48hrs, and now the fault is reoccurring.

Does anyone have any idea what might be causing this fault as replacement PCBs are not cheap or easy to come by!

I have tried the Gledhill tech support but can't seem to get anyone to answer the phone, and emails direct you to the phone line.