Boiler Firing Up Only When Water Needs Heating

I had an interesting little query about my own domestic boiler the other week.  I noticed one afternoon that the boiler hadn’t been firing up – I couldn’t remember hearing it do so and decided to investigate.  The timer was illuminated to show that HW (hot water only) timer was doing it’s bit.  So to see if there was a fault, I pressed the override button on the CH (heating) side and up fired the boiler.  Well, this rather pleased me.  Good idea ….  at least I know the boiler is not on the blink.  Thinking I’d be without any hot water, I left the CH firing up nicely.  It got rather swampy in the house after an hour as it was the weather to have the heating on!  I mentioned this business to a pal – he has a completely different boiler system and started to blind me with science over how this works and that!  He did however suggest I check if the emersion heater still worked on mine.  Of course – I’d forgotten I had one.  I never use it but yes, it started to hum gently as soon as I depressed the wall switch.   As it happens, I didn’t have a boiler problem.  My very effecient and helpful boiler service contractor pointed ou the lack of firing was simply because I already had lots of hot water left in the tank – I don’t use anywhere near as much as I used to – my way of helping the planet.