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A difficult Heatmaker service call
Had a customer this morning with a Heatmaker HW-M2 (Mark II). They had hot water, but poor heat from their baseboard. There was no voltage going to their circulator (the one outside the boiler, not the one inside the boiler). After quite a bit of tracing wires and using my VOM, I suspected a bad low limit.
The Heatmaker low limit is basically a strap-on style aquastat with three wires. Two wires go to the board, and if I jumped those out, the burner would come on. The third wire goes to a relay, which activates the external circulator. I could only get voltage at the circulator by jumping all three wires together.
I replaced the low limit switch, but still no voltage at the external circulator. I thought that maybe the new switch was defective, so I tried a second new switch. This time, the burner came on, but still no voltage to the external circulator.
This doesn't make sense. I got voltage to the circulator when I bypassed the low limit, so that would indicate a bad low limit. But what are the odds that two new replacement parts are bad?
I considered the possibility that the board might be bad, but the replacement board that came with the service parts kit for the Heatmaker had a connector for the secondary that didn't fit with the connector from the transformer. Therefore, I didn't get to rule out a possible bad board.
Long story short, I failed to get the heat back on.
Was there anything else I should have checked in my effort to find out why no voltage was getting to the external circulator? Or did I just use the wrong method to check the limit switch (especially since I'm used to a 2-wire limit switch)? The service manual for the Heatmaker is not that easy to follow, in my opinion. I'm stumped!