I read with interest cloves, ballvalve, and other comments in the HVAC thread on using polaris hot water heater for both dhw and radiant heat system. I installed a polaris last January and it provides hotwater for both my heating system and my dhw needs. I have three zones, two mixing valves(one for the cement floor zone). My system is 1/2 PEX with steel defuser plates under the upstairs floor. The system seems to work well, although I haven't had the upstairs heat on during a 30 below stretch yet. Anyway, my only concern is my polaris fires up almost every 15 minutes, runs for about 30 seconds and then shuts off. It did this all summer when there was no demand for radiant heat. My question is: Is this normal, if not, what should I do to keep the water heater from cycling so often? I am worried about burning out the igniter or other parts of the hot water heater control system. Just for your information, the heater runs fine when there is a demand on it, either for heating or dhw use. It seems like it cycles often only during the periods when there is no demand.

Any help would be appreciated.