This is a Worcester Greenstar combi boiler I serviced this morning. It is in a loft space, and it is still running at zero system pressure. Great, as the customer doesn’t get interrupted for low system pressure!
Unlike most boilers from other boiler makes, most of Worcester boilers don’t have a low water cut out mechanism which makes them look more reliable than other boilers, but once a main heat exchanger has full of air, as this is quite possible for a boiler in loft space which is the highest point at a heating system, the boiler will be dry fired.
My suggestions to a combi boiler in a loft space are: 1. don’t choose Worcester. 2. Get it serviced on annual basis, to make AAV working for air to get out. AAV = Auto Air Vent
It is just an approach chosen by Worcester, ie, a boiler is designed to have fewer minor troubles than others, but once it goes wrong, it is like a motorway accident, a new boiler might be required.
Vaillant boilers have a low water pressure sensor to cut off boiler running if the system pressure is lower than 0.5 bar. Baxi / Potterton and Ideal boilers have low pressure switches.