Couple of times yesterday our boiler (Grant Vortex Eco) started up when
it shouldn't have (timer-controller in 'off' phase for both HW and CH,
no tell-tale 'on' lights on).

Only came on for a couple of minutes, warmed up and then stopped. Normal
service resumed later when timer came on.

First thought was it went into frost protection mode by mistake (it's
not cold here). Not really anything in the manual about it (except the
bare mention that the boiler may have a frost protection stat or pipe
stat). How would one check?

--
Evremonde