When boiler fails to operate, 1st thing to check :  is it actually the boiler which has failed OR is it the external electrical call ( from the Room thermostat or the Programmer). Sadly our engineers are called out for properties where people don’t know how to operate their programmers / room thermostat.  Most of these cases are on rented properties. It is necessary that the landlords provide the user manuals for all the appliances & the controls ( such as Room thermostat & programmer ) to their tenants OR they will have to pay the price of unnecessary call out charges.