Hydrotherm 85 boiler - turning on signal contact issues ?


Old 03-10-12, 06:49 AM
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Hydrotherm 85 boiler - turning on signal contact issues ?


I have a Hydrotherm 85 gas boiler. It works fine for a 1-2 weeks or so, and then it stops working. The flames don't come on, even though the thermostat setting is at least 10 degrees higher the current temperature. I've changed the thermostat to another boiler, and that boiler works fine with it. I pretty much ruled out the thermostat issue.

So, then I looked at the thermostat wire contact point with the boiler. A picture is attached. What I did was to slightly unscrew the white wire that leads to the #2 contact screw and I started to tighten it and the boiler turned on. So, I finished tightening the screw. The boiler worked for about 10 days or so, and was working perfectly until it totally stopped working.

I can probaly get it started again if I mess around with the screw again. However, I'd like to get it permanently fixed. I don't like waking up at 3 AM from the cold temperature.

Any ideas ?

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Old 03-10-12, 07:59 AM
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Hi Acie!

Are you able to examine the wiring on the other side of that terminal strip? I would suspect that you may find a bad connection inside, if moving the screw around sometimes 'fixes' it.

The other thing is that it is possible to have a thermostat wire break INSIDE the plastic jacket insulation. Moving it around might cause the wire ends to touch again... for a while.


I don't want to sidetack this discussion, but I'm going to place some links to your previous posts for historical purposes... these are only for reference so that we know where ya been with the old gal...



Old 03-10-12, 08:47 AM
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That terminal strip goes to the gas valve/ aquastat. Hydrotherm put it there as a convienence. It runs inside the jacket.

Mike NJ
Old 03-18-12, 06:16 PM
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Join Date: Dec 2010
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Thanks for your suggestions.

I had a chance this weekend to look at the other side of the terminal. Everything looks normal. What surprised me is that the screw is not touching anything but is maybe an 1/16" away from a small amount of metal shaped as a small tear drop. The other screw has a similar setup.

When the heater is not working I woud unscrew the #2 terminal screw and moving the wire on the body of the screw until would make contact and the flames would go on. Then I would carefylly hold the wire in place and tighten the screw to the terminal(with the wire looped around the screw between the screw head and terminal.. Hoping to keep the contact in place, which it does for a week or so until it stops.

My gut feeling is that either the wire and/or the screw stops or loses its contact sensitivity with each other? I don't know if I'm making any sense.. However, the screw is always tight when I go to untighten it...just strange...
Old 04-03-12, 12:10 PM
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Join Date: Dec 2010
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My update. I removed the jacket of the boiler and folowed the wire from the entry point of the boiler(back of boiler) to the boiler's front connection point.
I didn't find any visible issues. I unscrewed all the screws and re-tightened them, making sure there is plenty of wire wrapped around the inside the screw head for proper contact.

The result, now instead of breaking down every 2-3 weeks, it now breaks down every 2 days or so.

I'm thinking of buying a new thermostat wire to attach it to the existing wire where the thermostat is and pulling it from near the boiler, and hopefully I can easily replace the thermostat wire.

Any other recommendations besides replacing the wire ?

Any specific type of good quality wire that I should get ?


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