Boliermate II - inconsistent hot water

Having a few problems with getting hot water from our Boilermate II at the moment. Just had 4 days without water, then 3 with, then 3 without, then back working again today. I'm wondering if it's the settings we have in place or it's a genuine problem.

The water has been fine all winter with (Potterton Suprima) boiler thermostat set to full, almost full winter setting on Boilermate, and room thermostat set to 15 celsius overnight. Then just over a week ago, no hot water, but the boiler was firing as if it knew the store needed further heating. This was happening every 5 minutes but lasted only 30 seconds, so this was having no effect on the amount of hot water.

I decided to turn down the boiler thermostat and this seemed to give us hot water for 3 days (probably a coincidence).

Then we had the same boiling firing symptoms until I decided to turn down the setting on the Boilermate (i.e. less generous hot water) as I thought this might stop the boiler firing every 5 minutes. It did! And I was able to have a hot shower this morning.

Could these setting changes have any effect? If the symptoms come back again, I will be giving you a call to have a proper look!

Mike came over yesterday and immediately found the problem. We needed a new thermister in the boiler and now we have beautiful hot water, literally on tap!