Early Boilermate, boiler pump running continuously- SOLVED

I’ve been getting advice from Murray, just thought I’d post the solution to maybe help others.

Early Boilermate, was installed late 90’s, no pump drive PCB, oil fired Camray 3.

The boiler pump was running continuously, I sent Murray a faulty PCB I had for repair. Installed on return but no difference, so after emails with Murray I ordered a replacement tank thermostat. The new tank thermostat also made no difference. After further email with Murray, the wiring was all checked and looked good, then he spotted the new thermostat was set to 70+ degrees C. The new thermostat had a factory set temperature of 77 deg C for the Boilermate, Murray suggested this might be optimistic for a boiler that was 25 years old. So I reduced the thermostat temp slightly and it all works fine now. I tweaked the thermostat up to the point where the boiler pump wouldn’t stop running, then turned it down by a very small adjustment so it all works again.

The boiler (Camray 3) has a max temp output of 80 deg C, but I guess it’s performance has dropped off a little bit and it’s max output is now too close to the required 77 deg C for the tank thermostat. Although the boiler is 25 years old it works fine, it’s had a new motor and a coupl of new pumps, and it managed a net efficiency after its service in December of 88.3% so it’s in good shape yet.

My observations since the fix - the boiler isn’t kicking in as often, and when it does it’ll run a bit longer, clearly this is now down to the boiler being able to deliver water slightly warmer than the tank thermostat, and I also wonder if the boiler pump running continuously was maybe drawing heat from the tank a bit quicker than the normal tank heat loss.

Wouldn’t have sussed this on my own so many thanks to Murray for his patience and help.