Our Ideal Response 120 combi boiler has been suffering constantly dropping pressure for some time now and we thought this was because of the PRV. On Sunday though, the boiler started dripping underneath from multiple points and now won't fire up. An engineer took one look at it and said the heat exchanger unit needs replacing but this is expensive and I'm not convinced that is the problem as I've never heard of this part on any forums before. Is he right? He didn't even try to start it up and said if the PRV needs changing too they will do that when they get the heat exchanger unit in. This will take 7-10days....!