Hello I'm looking for some advice on a 17 year old boiler (BAXI 105 HE) & whether it's sensible to fix or replace. The issue yesterday started out as a leaking filling loop at the final check valve, which I replaced. When re filling the boiler it started to not hold pressure, a wiggle of the pressure relief valve initially didn't fix, but it appeared to resolve itself within an hour. Now there's an issue where hot water isn't flowing. Taking the front off again it appears as the push rod on the DHW Pressure Differential Valve has seized & not pushing the microswitch (Page 44, https://www.baxi.co.uk/our-boilers/...hash=2D0AD0223DC5AADA00F9C57AAC53F69A025066DA) Is it worth spending the money for an engineer to fix it, I imagine in the ballpark of £300. Or is it time to replace? Alternately, It does seem to be a straight forward fix. Is it something I could do myself as a competent DIYer. Thanks in advanced Rob