We had antifreeze put in heating pipes. No problems. We switched heating company this year. They said that we were almost out of anitfreeze and they added antifreeze. That was back in August of this year. Recently -- last few days -- we have noticed a tremendously loud and rapid tapping sound in pipes once they are all heated up. The guy from t he heating company says it is not the boiler and has not figured out what is causing it but speculates it might be antifreeze. Any thoughts?

When it comes to antifreeze there are many different types and I hope you have the correct one for your boiler system. The wrong type can act as a acid and really cause problems. The tap sound sounds like a expansion problem and you might want to get that checked into by your service company. There is not much a homeowner can do with a sealed antifreeze system.

Since the heating company you use cannot figure it out I suggest you get a second opinion by trying a different company that has more experience in your situation.

Noises are something that cannot be diagnosed unless you are there to hear it and be able to make adjustments to the control circuit. The first thing I would do is lower the temperature of the boiler till the noise stopped. That will prove if it is a boiler problem or not. Then go from there.

If your boiler repair person has not tried this then he should not be in the business of working on boilers and that is why I told you to get a different company to give you a second opinion. BTW Different types of antifreeze have different boiling/expansion charteristics that can and do cause problems especially if they are improperly mixed.