Most of the units we have serviced over the years have been neglected, i’m assuming people think( if it’s still working – then its fine). But i’m sorry to say that’s no correct. By the time we got to these jobs most of the boilers were ready to be replaced with new ones and had badly aged from the inside out due to no inhibitor (anti rust) in the system or the same water had been in the sealed closed loop system (hydronic heating system) for many years without being replaced and flushed out. Some of the worst systems had a soup like consistency to them and rusty color to what used to be water with inhibitor in it. All gas appliances should be serviced at least once a year to keep you and your family safe, don’t take any risks with gas.