I've a Ferroli Modena . It starts off fine both in CH & HW mode but after about two minutes every thing shuts down (the fan, the pum etc). The demand for the CH led says on. It stays in this conditions for about 5 minutes then comes back to like for about two minutes and then locks up again. I've checked both of the safety thermostats and they seems to be okay. Any idea as what is causing this. THANKS.