We put in a new 12,000 gallon saltwater fiberglass pool in 2016 In Colorado. The contractor put in a Mastertemp 250. We started having some issues with it last spring so we thought we would be proactive and replace it. We had a local pool company who did routine maintenance quote us a new one but said they could not get one in a timely manner due to supply chain issues. Found a Mastertemp 250 HD from a on line pool supply company and paid the local pool guys tI put it in. The heat exchanger failed in the first 2 month. Went round and round with Pentair and even sent my water analysis reports from a pool supply house where I take my water to get it tested. They agreed to send out their approved pool service rep company to diagnose it. They too said heat exchanger failed. Pentair agrees to warranty and replaced entire heater in August 2021. Now less than a year later starting to see the same issues. Error code EO5 comes on and had a pool service company replace the the flue sensor a few months after it was put in and now they are saying could be the mixing valve. If not the mixing valve, then heat exchanger is sooted up and they say unit needs to be replaced. This would be the third boiler in 2 years and who knows if they will warranty again. We went with the HD because of the Cupronickel heat exchanger and from everything I read seemed to be a good choice. Just looking to see if anyone else has had bad experiences with these HD units or any suggestions as to why this keeps happening?