Complete Heat Replacement

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Dan H... Thanks for the kind comments! I've tried to understand the CompleteHeat to keep it going as long as I could, and then pass on what was discovered.

First, I think that you have correctly diagnosed the current problem "... now the HM30 needs a circulator pump as evidenced by varying shower temps and over-running heat limiting out the temp activated gas shut off. " The circulator pump is the key item in keeping the HM30 operating and your symptoms are the same as I experienced.

Next, "Might need a new gasket at the top of the tank too." I'd put off changing the gasket at the top of the tank unless you have a natural gas odor when the HM30 starts up. These gaskets tend to crumble after being in use a while - don't pull the gasket unless you have a new one in your hand.

Next "I looked on ebay for the taco pump and there are several 006 models offered. Could I just pick up any 006 model since I'm only using the inside cartridge?" You are correct, I suggested getting a 006 Taco pump on ebay since it is easier to get a whole pump at a reasonable price than just the less common cartridge - just get the best price you can get and use the cartridge.

next... "Your suggestion for the AO Smith Vertex looks good too but I thought the domestic and heating water systems were separate in the HM30. Would the Vertex solution run potable water thru the AM30 handlers and if so are there any lead solder considerations? " In the HM30, potable water is heated in a common tank and distributed to either the DHW or the space heating (in the AM30) as needed. There is no separation of water for the different functions. I think that there should be no lead problem with the 12 year old HM30 system - a new heater should not fundamentally change your exposure to lead since the same processes would be used in the HM30 and the Vertex.

The Vertex would be a good match to use with your AM30 since you stated "...HM30-100 has given us very good service for almost 12 years in a 2,500 SF two-zone home..." Your two-zone systems (with, I assume, two pumps and maybe two AM30 heat exchangers and electronic controls) would not require changes when using the Vertex, a great plus!

Next "For the Vertex did you use the Lennox PCB and what wiring change did you make?" I used the Vertex straight out of the box and just removed the HM30 water heater. The Vertex has its own controls that attempt to keep the water at the top of the heater at an even temperature; when water is used for DHW or in the AM30(s) the water in the tank cools and, when necessary, the Vertex initiates a heating cycle - just plain water heater processes. Looking at the electric schematics for the HM30 and the AM30 there are realy only seven connecting wires - 2 for 120Vac, 2 for 24Vac, a common, and two for handshaking between the AM30 and HM30. Reviewing the wiring just now, I find that what I did was remove ALL of these seven wires at the AM30 control board and it worked without any changes when used with the Vertex.

Lastly, "...I'm a doit-u-selfer for a long time and would like to avoid another HVAC house call. Last guy said he didn't know what was causing the problem and recommended changing EVERY servicable part." The HM30 is a real mystery to most HVACers which often leads to change-every-servicable-part recommendations, I suspect.

Hope this was useful for you Dan.

JohnP