So I've got a natural gas Viessmann boiler hooked up to my radiant hot
water heating system. I'm currently having an intermittent problem.
The thermostat is set at a certain temperature. The home temp drops
and the thermostat calls. The boiler temperature is hot but the
circulator pumps don't get turned on. If I leave it, it stays in this
state. If I reset the boiler with the on/off switch or winter/summer
switch then the circulator pumps start up. I watch the boiler temp
lower, the boiler turns on and heats the water and the cycle of pump on
and off starts. Eventually the house is at the right temp and
everything is ok, for a while. Then a couple days later I'll find the
temp has dropped again and it's the same problem: water is hot but
pumps are not turned on to circulate.
Anyone ever heard of a problem like that? The switches are set to "on"
and "winter" on the boiler. I've checked the current / voltage to the
pumps while they are not circulating and it is definately zero. So the
Viessmann boiler doesn't seem to turn on the circulator pumps.
What could be broken?