Don't understand why our boiler keeps firing up within a Megaflow heating system

[mr_jRayet]

Looking for advice here:

We have just moved into a new house (7 years old) where we have two boilers connected to a heating and hot water system. We have two thermostats on each floor and a electronic timer to start and stop the system of hot water and heating. In our airing cupboard we have two Megaflow tanks which I guess contain the hot water.

What we cannot understand is why when we swith off all the heating an hot water our boilers (well one of them) fires up perhaps every 15 mins for 25-30 seconds and then turns off - even when we think we have turned everyting off - also it looks like we have continuous hot water which seems wasteful of energy. I guess the megaflows provide us with the good pressure we enjoy and hence I understand why they also continually hiss as it seems they are on.

Looking for anyone who can shed light to our potential misunderstanding on how our configuration works. Note as of yet we have never seen the second boiler light up, even when we turn on the heating and thermostats

[John Stumbles]

If you have a Megaflow (or even two!) you should have it serviced annually by a qualified (for unvented heating systems) engineer to ensure that the safety systems are still working properly. Sounds as if you could do with a visit from someone clued up to check out your system. By all means get clued up yourself to find out what's going on, but unvented systems carry a risk - very very remote, but if it happens very very severe - of a steam explosion if things go wrong, so do get it checked out professionally. If you can afford a house with 2 boilers and 2 Megaflos, you can afford to have it serviced!