King Electric hydronic heater not working


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Old 02-06-21, 10:48 PM
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King Electric hydronic heater not working

Hello,

I recently purchased a home with a King electric hydronic heater (model HME 812-8/11) with a tankless water heater. The thermostat (model HWPT-120) isnít turning the system off when switched to the off position. I replaced the thermostat and it still doesnít turn off. What could be the cause and the fix? Any help is appreciated.
thanks!
 

Last edited by PJmax; 02-07-21 at 05:11 PM. Reason: turned on instant email notification
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Old 02-07-21, 01:01 PM
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Welcome to the forums.

You have a hydronic wall mounted fan coil unit and a tankless heater.
Not a common system.
Do you know what the line voltage thermostat is connected to ?
Do you have a circulator pump?
 
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Old 02-07-21, 05:14 PM
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Set your thread to instant notification so maybe you'll get a quicker response.
 
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Old 02-07-21, 06:17 PM
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Hi,

I'm realizing it's not so common, I can't get anyone to come and look at it lol.

The line voltage is 110V. Yes, we have a circulator pump.

Thank you,
 
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Old 02-07-21, 06:25 PM
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It shouldn't be that involved. The wall unit has a fan in it. That fan may be controlled by a thermostat inside the unit so that the fan comes on when it detects hot water. That would mean that your thermostat controls the circulator pump. When the pump starts..... the water starts heating.... when the coil gets hot.... the fan starts.
This is one way of controlling that system.

There must be some type of control relay by the boiler and the pump.
Post some pictures for us to see what you have.. How-to-insert-pictures.
 
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Old 02-07-21, 06:47 PM
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Last edited by PJmax; 02-07-21 at 08:01 PM. Reason: reoriented/resized pics
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Old 02-07-21, 08:06 PM
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Good pictures.
Are there just two wires connecting the fan/coil unit. White and black ?
I see two red wires in the thermostat box connected to red.
How many black wires in the thermostat box..... are there three in that splice ?

So far the mystery is where do the two red wires go.
One surely goes to the pump. I can't tell where the other one goes to.
 
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Old 02-07-21, 08:50 PM
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Yes, there are just two wires coming to the fan/coil unit, White and black
Yes, the thermostat's red wire connects to two red wires coming into the thermostat's box. Keep in mind that the system has one circulating pump that feeds three fan/coil units. Each fan/coil unit is controlled independently by its own thermostat. Is it possible that the red wires that come to the thermostat box are in series?
The thermostat's black wire is connected to two black wires that come to the thermostat box from two different directions. There are three romex cables coming to the thermostat box two of these have black, red, white and ground wires, and the third one just black white and ground. I am pretty sure the last one feeds the fan/coil unit of this room. I don't think my unit has a temperature probe to keep the fan running as long the coils are hot, UNLESS the red wire attached to the "high/low" switch of the fan/coil box is the temperature probe

 
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Old 02-07-21, 10:45 PM
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Oops! minor correction: there are three wires coming to the fan/coil unit: black, white and ground.
 
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Old 02-08-21, 12:38 AM
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It sounds like the three wire cables loop between units.
That would indicate..... black is hot, white is neutral and red is switched to the circulator.

You didn't originally mention multiple fan coils and since they share one pump..... each thermostat needs to activate the pump and turn on the fan.

If that is correct..... is it possible that you miswired at the thermostat location ?
It would make sense that the black from the two wire cable go to yellow on the thermostat.
Since the fan/coil black wire is connected to always live..... it won't shut off.

 
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Old 02-08-21, 03:28 PM
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Your guess matches that of the manufacturer. I looked at all thermostat boxes and the wires are spliced according to their colors, so I don't see any obvious problem. However, it appears that a wrong connection burns the thermostat in question. If it is not a wrong connection, it may be a damaged wiring inside the walls, although it is a 4-5 year old installation and the wires are new.

One thing that bothers me is that there are no separate valves to be controlled by each thermostat (at least that I can see). If one thermostat calls for hot water, it activates the circulating pump and hot water runs through the system. I don't understand how the hot water is directed to the unit whose thermostat asked for hot water.
 
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Old 02-08-21, 07:12 PM
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Correct...... no separate valves. Water flows thru all coils at the same time. That is why each thermostat needs to control the blower in the fan/coil unit and the way I see it wired.... it won't do that.

I would severely doubt you have a shorted cable in the wall.

Is it just the thermostat in the picture that has the problem ?

 
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Old 02-08-21, 08:16 PM
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Yes! If I disconnect the yellow wire, I can turn on the breaker of the circulating pump and the other two units would run fine. I suspect though that the way the wiring is set it burns/destroys the thermostat in question.
 
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Old 02-08-21, 08:33 PM
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I just went back to look at the pictures. Does the black of the two wire cable currently connect to the yellow wire on the thermostat ? I can't see it in the picture.

If yes...... when you disconnect the black from the yellow the other two thermostats control the pump and their own fans correctly ?

So with the black and yellow wire disconnected..... when you call for heat from this thermostat the pump does start correctly ?

(when wiring count is discussed..... ground is not included)
 
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Old 02-08-21, 08:59 PM
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Yes, when I disconnected the yellow wire in the the thermostat box, I could turn on again the breaker of the circulating pump and the other two units were running ok and the fan of the problematic unit does not run.
 
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Old 02-08-21, 09:06 PM
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So as soon as you connect the black and yellow..... the fan comes on ?
Even if the the thermostat is off..... the fan still comes on ?
That is a new thermostat and the old one did the same thing ?

King HWPT120 instructions (pdf)
 
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Old 02-08-21, 09:31 PM
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YES! In fact, when I connected the new thermostat and turned on the breaker the fan did not start. Before screwing the thermostat back in its box, I tested its ability to control the fan and the recirculating pump and it appeared that I had fixed the problem. I screwed the thermostat back to its box, but I don't recall if the problem reappeared before or after I turned on the other units. I think now I have toasted the new thermostat. As if I knew what would happen, I purchased two thermostat, so I still have an unused one that I save until I know that the wiring is correct.
 
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Old 02-09-21, 10:37 PM
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Well, today an electrician came to help with the troubleshooting and we were on the phone with an engineer from the manufacturing company the entire time. To make a long story short, the new thermostat that we had installed was faulty. We could not find anything wrong with the wiring connections. When we reinstalled the old thermostat that was causing problems, miraculously the system started working as it was supposed to. The good thing is that the system has been working properly for the last ten hours. The bad thing is that we have no explanation as to why the old thermostat had problems.

Nevertheless, we greatly appreciate the help we received from doityourself.com. Pjmax you are an exceptional person. We don't have enough words to THANK YOU!
 
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Old 02-10-21, 04:41 PM
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You are very welcome. Thanks for letting us know the final outcome.

In fact, when I connected the new thermostat and turned on the breaker the fan did not start.
I believe the fan is on a 1 minute turn on delay. This gives a little time to get the hot water moving before the fan starts.
 
 

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