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Old 02-17-2019, 11:04 PM   #1
Ali
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Hydro-Hot 2001-E > hot water works, but no room heater fans or pumps are running

Hello everyone,

We are having a strange problem with the hydro-hot 2001-E unit on our 2000 Monaco Windsor. The hydro-hot fires up, stir pump works and we get very nice hot water coming out of our faucets, but no action on any zone heaters.

We have 3 thermostats in our coach, and they are all set to high 80 degrees. The hydro hot unit cycles on and off as we use the hot water, but there no action on the room heater fans or the circulation pumps on the hydro-hot. It acts as if the thermostats are off and no zone heating is needed. I am thinking either the thermostats are not sending the unit signals to turn the circulation pumps and room fans on, or perhaps the relay is broken or a fuse is blown, but I cannot figure out how to troubleshoot this issue.

Any help would be greatly appreciated.

Thank you.
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Old 02-18-2019, 01:30 AM   #2
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I'm sure others will chime in as well but it is common for the check valves on the circulation pumps to stick closed. The pump will run but cannot circulate the hot water.
Generally a quick rap on the top of the check valve will cause it to open and then the water should circulate. I used the handle of a large screwdriver to hit the top of the check valve and it opened.
Good luck.
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Old 02-18-2019, 05:27 AM   #3
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I agree with you, Ali. It sounds like the thermostats aren't talking, as it doesn't sound like the Hydro-Hot even knows it is being called upon for space heating. If the Hydro-Hot is like our Aqua-Hot, there is a control board with a long row of wire connections on each side of the board, and they are fairly well labeled. Also, the control logic on that board is pretty basic.

You said that your heat exchanger fans are NOT running, AND you are sure the circulating pumps are NOT running. If both of those conditions are true, then either the thermostat signals are not coming to the control board, or the control board is not working properly.

On our AquaHot, the top two-thirds of the left side strip of connectors is dedicated to the zone heat exchanger fans and the thermostat inputs. They are labeled "FAN +", "FAN -", "THERMO-O" and THERMO-I". The two FAN terminals provide power to the heat exchanger fans. When the zone is not calling for heat, the voltage across those two terminals should be zero volts, and the exchanger fans should not be running. When the zone is calling for heat, the voltage across those two terminals should be approximately 12 volts, and the fans should be running.

The easiest thing to check first, at the circuit board, would be the inputs from the thermostats. Each of your thermostat inputs should look like a simple switch, to the Hydro-Hot control board. If your board is as I have described, with the terminal labels like I have described, you can "pretend" you are the thermostat and just "short" the two "THERM-O" and "THERM-I" terminals with a paper clip or a jumper wire. When you short those two terminals together, your circulating pump should immediately start running and the respective heat exchanger fan should start operating. If the appropriate pump starts running, and the appropriate heat exchanger starts functioning, then the problem with the thermostat(s), as you will have just confirmed that if the thermostat calls for heat, the Hydro-Hot is doing its job properly. You can work your way down that terminal strip and check each and all of the zones.

I will stop here, to keep this from becoming too long. Also, it may be that your Hydro-Hot is sufficiently different than our AquaHot that my information may not be of any value. I will await further input from others that have more model-specific information, and from you.
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Old 02-18-2019, 08:44 AM   #4
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You have 3 thermostats, or a thermostat with 3 zones, like we do?

Like I said, mine has 3 zones, but only zones 1 &3 have 'furnace' modes. If I were to set zones 1 & 3 on 'furnace' at 80*, and accidentally left zone 2 on'Heat pump' at 80*, my AH heating would never come on.
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Old 02-18-2019, 11:21 AM   #5
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Ali, do you still have the original Dometic 4 button thermostats? These can be troublesome.
Have you replaced any of the AC units recently? The thermostat controls the Hydro Hot through the control board on the main AC.
Has the heat portion of your Hydro Hot ever functioned?
The reason I ask is the 2000 Windsor brochure describes it as an optional "Hydro Hot Water System".


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Old 02-18-2019, 09:49 PM   #6
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Quote:
Originally Posted by Topman View Post
.. it is common for the check valves on the circulation pumps to stick closed. The pump will run but cannot circulate the hot water. Generally a quick rap on the top of the check valve will cause it to open and then the water should circulate. I used the handle of a large screwdriver to hit the top of the check valve and it opened.
Thank you Topman, appreciate the tip on the check valves. I checked the controller today and found out, its not sending 12v to the circulation pumps, so it seems like a controller issue.
BTW, I noticed you are from Abbotsford. We were there just a few months ago, got a few repairs done with our blue bird at the First Truck Centre. You guys have a nice coach, same year as ours but you have the best Monaco has to offer. May I ask how many miles you have on the Exec? Thank you.
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Old 02-18-2019, 10:02 PM   #7
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Quote:
Originally Posted by K7JV View Post
..The easiest thing to check first, at the circuit board, would be the inputs from the thermostats. Each of your thermostat inputs should look like a simple switch, to the Hydro-Hot control board. If your board is as I have described, with the terminal labels like I have described, you can "pretend" you are the thermostat and just "short" the two "THERM-O" and "THERM-I" terminals with a paper clip or a jumper wire. When you short those two terminals together, your circulating pump should immediately start running and the respective heat exchanger fan should start operating. If the appropriate pump starts running, and the appropriate heat exchanger starts functioning, then the problem with the thermostat(s), as you will have just confirmed that if the thermostat calls for heat, the Hydro-Hot is doing its job properly. You can work your way down that terminal strip and check each and all of the zones.
Wow, thank you Jim, really appreciate taking the time writing such a detailed response. I did a few tests today, including jump wire the thermostats and nothing, it didn't trigger the pumps or the fans. I also checked the thermostats themselves and they all seem to work. I guess my nightmare is coming true, it seems to be the controller. I also checked the controller up close, looking for anything burned but I couldn't spot anything unusual. I noticed there are a few micro relays on the controller, I am wondering if one might be a main relay which does not close anymore. In either case, I think I am going to order a replacement controller and try to replace it myself.
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Old 02-19-2019, 05:14 AM   #8
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Good morning, Ali

Here is a link to the service manual for at least one model of the HydroHot, and I suspect it will be mostly if not completely applicable to your unit.

http://www.aquahot.com/files/service...anual07-03.pdf

Start with page 33 and see if it might give you a few things to check before you make the plunge for the new board. Also, AquaHot should be able to help you. They are at Aqua-Hot Heating Systems for RV, UTV, RTV. Unfortunately it looks like they are in the upper three-hundred dollar range, so hopefully you won't have to. But I agree that there is a fair chance that is where your problem lies.
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Old 02-19-2019, 02:10 PM   #9
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Check this sensor,

Check this sensor, I just had the same issue, good hot water but no heat, no pumps or fans inside the coach. This sensor was bad and it is supposed to cut off interior heat. I copied this from a manual and if you have your manual it is easy to just jumper this sensor, just find the proper terminals.

Low-Temperature Cut-off Thermostat:
The Low-Temperature Cut-Off thermostat operates the domestic hot water priority system by blocking the interior
heating feature when domestic hot water is being used. This
ensures that even heat is provided for domestic hot water,
which avoids the possibility of cold water pockets during
showers,.
Troubleshoot the Low-Temperature Cut-Off thermostat if the
following conditions have occurred:
 There is a lack of interior heat.
 There is a lack of hot water and the “Low Temp Cutoff
Status” indicator light on the electronic controller continuously remains illuminated, which does not allow the
stir pump to operate.
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Old 02-23-2019, 08:02 PM   #10
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Quote:
Originally Posted by PlanBee View Post
Low-Temperature Cut-off Thermostat:
Check this sensor, I just had the same issue, good hot water but no heat, no pumps or fans inside the coach. This sensor was bad and it is supposed to cut off interior heat. I copied this from a manual and if you have your manual it is easy to just jumper this sensor, just find the proper terminals.
Thank you, PlanBee You are correct. We were having the same exact LTCO thermostat issue
I bypassed it, and all is working now. I am ordering a replacement thermostat. Happy to have the coach heating back on
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Old 02-25-2019, 12:49 PM   #11
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Quote:
Originally Posted by Ali View Post
Thank you, PlanBee You are correct. We were having the same exact LTCO thermostat issue
I bypassed it, and all is working now. I am ordering a replacement thermostat. Happy to have the coach heating back on
I'm glad I could help. I thought it might be that sensor. I also found if you are winterized and the water is blown out of the system the sensor won't get hot enough to allow interior heat, once the coach is hooked to water it would work fine.
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