Ultraheat Tank Heater Pad Issue

[Raywatt]

My converter fan is running continuously when I switch on my 2 forward UltraheatTH-624 heat pads. When only middle TH-1218Ultraheat and rear TH-624Ultraheat heat pads are on the inverter fan does not run.
The 2 front tank heat pads are switched on by one red lighted interior switch and middle and rear tank heat pads are on the other red lighted switch mounted top and bottom on wall in kitchen area at rear of trailer. The converter is located near middle of 33' 2005 Dutchman Colorado by Thor trailer. All 4 tank's heat pads have been on for three days with no change. Ultraheat pads are engineered to turn on at 44* and off at 64* allowing tollerances of plus or minus 10* which seems excessive to me.
AC plugged in and have underbelly down.
So far have:
1. Removed small patch of paint from frame and reattached main grounding wiring lugs, cleaned and tightened all grounding contact points.
2. Swapped red lighted interior on/off tank heat pad switches. Each switch operates 2 tank heaters. Top Switch Grey#1 and Black tanks. Lower Switch Fresh Water and Grey#2 tanks.
3. I have cut the hot wires to each mis-behaving TH-624Ultraheat Pad on forward Grey#1 and Black tanks and done many 12volt attached and detached on/off testings. Converter fan runs at the same speed whether only forward Grey#1 TH-624Ultraheat Pad is operating, or only second tank back Black Water TH-624Ultraheat Pad is operating, or when both Grey#1 and Black Water UltraheatTH-624 heating pads operate together simultaneously.
4. Volt readings taken while checking wiring at each tank for 12 Volt power: Grey#1(11.8 volts), Black Water(11.8 volts), Fresh Water(12.6 volts), Grey#2 (12.8 volts)
5. Tank Temperatures front to back taken with Infrared Thermometer when outside temperature is 38* to 44*
#1 Grey TH-624 Ultraheat Pad: 59*, Outside of Tank 43*
Black Water TH-624 Ultraheat Pad 71*, Outside of Tank 44*
Fresh Water TH-1218 Ultraheat Pad 56*, Outside of Tank 46*
#2 Grey TH-624 Ultraheat Pad 48*, Outside of Tank 44*

Converter fan also runs continulosly at temperatures 44* and up when two front heat pads switched on.

Suggestion from Ultraheat and RV shop was to run new 12 gauge wiring from 2 forward TH-634 Ultraheat Pads to upper switch. Reasoning being there might be resistance build up in long wire runs. Would this really work and be worth the effort? Would be very difficult to run wire as present wire from switches is incased inside of wall between Refrigerator and Gas Stove inside inaccessible black plastic flexible split loom tubing. All wire appears to be 14 gauge and OEM which I would think was designed to be sufficient to operate all Ultraheat pads together when trailer was built. Running new wire would require having to do some (most likely) very difficult wire fishing. Going to try by-passing switch and temporary hard wire 2 front heat pads directly to converter and see what happens.
As RV store pointed out, if boon docking in freezing temperatures with front 2 Heating Pads running continuously on batteries, charge would drain down quite quickly.
Any suggestions or ideas appreciated.

[Raywatt]

I don't have a clamp-on ammeter but will check around to see if any friends have one. I suspect the rear heat pads may not be workin as infrared thermometer readings are a bit lower than front 2 heat pads. Defiantly may need to be cooler outside for rear pads to come on. According to tech at Ultraheat: heat pads generally will come on near 44* but there is a 10* allowance for on/off. The fronts run converter fan 24/7 no matter outside temperatures and that is baffling me.
To Dougrainer, I looked up ambient sensor probe but not sure what this device does and how it would be incorporated into my system. The way Ultraheat tech describes on/off is there is a small metal block mounted/inserted in the foam of heat pad that contracts to create electrical connection to turn on heat pad at around 44*.

[time2roll]

deleted

[dougrainer]

Are you positive you have the optional ambient sensor probe system installed? Doug

[time2roll]

As it appears you have access to the pads I will suggest a clamp-on ammeter will tell you exactly what is going on as far as what is working and how much power they are pulling. Very possible those rear pads are not getting power or it just needs to be a bit cooler. Yes the converter fan will run continuous when any of these 12v pads are activated.

I added 120v pads as I assumed I would be on utility power in these conditions.

[Raywatt]

Yes I am concerned forward tank heat pads are not cycling off and rear tank heat pads do not make converter fan come on at all during their cycles. Also don't like fact converter is always running and that this is happening on forward tank heat pads but not rear tank heat pads. Newbie posted to see if there might be suggestions for finding issue or if someone has run into similar problem and has insight to what it may be. Relatively new to big rig RV'ing but did spend 6 moths in FL & AZ last winter but obviously didn't need or have to turn on heat pads. Have owned trailer a year and a half.

[pnichols]

Your 12 volt powered tank heat pads probably draw from between 4 to 12 amps (depending upon the size of your pads) when cycled ON. See their website here: https://www.ultraheat.com/ultraheat-rv-tank-heaters

However of course, they're not ON drawing battery power full-time in cold outside air temperatures - they cycle ON and OFF keeping the tank wall at an average above-freezing temperature during cold weather - so the current they pull from your batteries per hour is not the constant amount shown in the UltraHeat website specifications. Due to their ON and OFF cycling, the average current drawn per hour will be less than what the specifications show on the website.

With plenty of solar power and daily sun or with daily generator runs - to recharge coach batteries - you should be able to keep your tanks from freezing when drycamping in cold outside air temperatures.

Use of these pads seems like a no-brainer to me as compared to messing around with anti-freeze in the tanks, or worse yet ... not using RV tanks and their plumbing during cold weather. We've had the 12 volt version of these heaters on our RV's tanks for years - just in case.

[dougrainer]

EACH pad pulls about 12.5 DC amps. So, if the wiring TO the pads is smaller than 12 gauge the amp draw will go up and use more dc voltage. Doug

[GordonThree]

Trying to boondock with electric heaters sounds like a real uphill battle.

It's been my experience a frozen tank isn't that big of a deal, but rather the dump valves freezing. It's also been my experience heating the tanks alone doesn't keep the valves from freezing. I ended up wrapping mine with aluminum, heat trace, more aluminum and then gorilla tape to protect everything. Heat trace takes minimal wattage when run off my inverter.

[time2roll]

Are you mostly concerned that the converter fan is running? That would be very normal running tank heaters.

Or are you concerned that the heat pads are not cycling off? With the outside of the tank in the 40s I would expect the heaters to be on.

Possibly check the amp draw to each pad with your clamp-on DC ammeter. I don't think larger wire is going to help unless you need more heat and this will only draw more power.

You really need utility power, run a generator 24/7, or plan to let the tanks freeze when camped in these conditions.

Raywatt wrote:
5. Tank Temperatures front to back taken with Infrared Thermometer when outside temperature is 38* to 44*

While in use the tank heaters can stay off until you get below 30° F.