seasonally eratic thermocoupling

ScottSS

We have a hydronics system that uses a heat exchanger to draw heat from our 75 gal. (American Water Heater, 75000BTU) water heater. During the months that we do not heat the house, the water heater operates normally. But when we run the hydronics, the thermocoupling seems to both turn on and shut off the burner at much lower temperatures for the same setting/mark on the dial, thus requiring us to turn the setting to max, as well as turn off the hydronics, before taking a shower. We have replaced the thermocoupling once, but the new one behaved the same way. We drain the tank once a year, but do not have a circulating flush kit installed. Any ideas about causes or solutions?

Unknown

Thermocouple has nothing

to do with temperature. Something else is wrong. That is unless the pilot is going out and that is what you equate to the thremocople causing water temp problems??? Really not sure what you are trying to say.

Jamie_5

tank mixing?

He seems to be saying that (1) the hot water coming from the tank is cooler when the heat exchanger is operating and (2) they are bumping up the thermostat to compensate. Perhaps the mixing that occurs in the water heater when the heat exchanger pump is operating is causing the water inside near the top of the tank to be cooler than when it is allowed to stratify. If this is the case and they have insufficient domestic hot water with the thermostat bumped up, I'd guess they are short on capacity, since the heating system essentially has priority. They may need to change the way the heat exchanger is piped and/or get a bigger or more powerful water heater.

That's my guess, at any rate.

TimS

it cant keep up

Try priority for dhw use an aquastat on supply to HX to shut off primary pump below a certain setpoint and install a mixing valve for DHW turn up water heater hotter. Theres more things you can do if you want to get fancy. $$ aside unlimited options for improvement.