We have a Boilermate 2000 in our house and up until now it’s been mostly acting fine. However a couple days ago I noticed that when turning up our thermostat the heating wasn’t getting as hot as expected. Following that I noticed that the regular boiler wasn’t starting up straight away but would seemingly come on for very short periods of time (30s to 1min) before going off again, and repeating this as time went on. Yesterday we didn’t get any heating whatsoever. The thermostat was turned up high but the boiler wasn’t coming on at all and all radiators were cold. I tried switching the Boilermate to its backup mode for heating and hot water, but when I first did this it tripped the central heating switch in the fuse box. I reset that and tried again and at that point it did work, although it didn’t really get much heat through the radiators. At first I thought it might just be a broken thermostat but now I’m not sure, especially with it tripping the switch.
I’m not familiar with Boilermate but have you seen this? Some advice on faults further down. https://boilermate-repairs.co.uk/boilermate-2000.html
I think the backup mode uses electricity only and is just for emergency use. We've got one and had to have the PCB replaced due to a similar fault, pumps and sensors can also fail.