Tha main issue with the boiler is, it’s crap, of a very poor design, the plate heat exchanger gets badly blocked and trips the overheat stat. Gled hill the manufacturer went bust in 2008 and all remaining stocks of heat exchangers have been used up. Nobody will provide a new service plan for them due to the issues, there is a website dedicated to the issues. It was a new build with corners cut ie no inhibitor that we bought as a repo in 2008, when we purchased all services were either cut off or inthe case of heating/water drained off, we have replaced a couple of radiators due to leaking at seams, been told prob due to a combination of no inhibitor at commissioning and being left drained for 10 mths. This is the house we want the kids to grow up in, good area, lots of outside space, small village, so want to do the upgrades right first time and not have to worry about stuff again till they move out.
The strange thing about the old boiler is that it has electric back up, a 9kW element to provide heat and water should the gas side fail, it’s like vw selling a T5 and giving you a polo on a trailer just in case you have a breakdown, they must have known it was a rubbish product when new.