In 2009, I solicited several bids for a high efficiency gas boiler with an indirect water heater. They were installed by a Carrier recommended contractor. After installation, he replaced, at no cost to me, the Taco zone valves because of a severe noise problem. He also made several service calls, at no cost to me, because of a lack of heat. During these service calls, he increased boiler temp to 200 degrees, which did nothing but decrease efficiency of boiler.He also took readings of boiler input & output temps which he would not disclose to me. Last winter, when outside temp dropped to 9 & 10 degrees, boiler ran for 18 hours just to satisfy one zone in a three zone home. I called in a tech from a different heating contractor to address the lack of heat & his analysis was that the boiler was undersized.When I informed the original contractor of this, he said he would replace the 100,000 BTU boiler with a 150,000 BTU boiler. My question is, Who should pay for the boiler & installation?

Unless you can prove to a court of law the current boiler is undersized, you will bear the cost of the new boiler & installation. Did either contractor do a Manual J (heat loss calculation)? If nobody has, everybody is guessing.