Our first RV Surprise – We have a Combo Water Heater… that stopped working

This one is a little embarrassing to admit but we just realized we actually have a combo water heater and not a propane-only one. When we bought it, I remember being told it was a propane powered water heater and I guess we took that at face value.

How did we find this out? We have been using it on propane and it has been working for a while. It started deteriorating in performance over the last few days and yesterday, it stopped altogether. While researching repair and maintenance tutorials and youtube videos, we learned about what all the different knobs, switches and parts were and lo and behold, our water heater includes electrical heating mode which functions independently of (or combined with) the propane heating mode.

We have a Suburban propane/electric combo water heater (SW6DE) and neither the propane not the electric heating worked.

Of course, as part of troubleshooting, we took to learning a bit more about how these components work.

Electric Heating Mode – Suburban Combo Water Heater (SW6DE)

The electric heating mode on this water heater works off the 110V electric system, i.e. it is powered when the RV is plugged in. Some important components of this system and information that might help you troubleshoot:

• There is a fuse for this in the fuse box under the stove. This is one of the first things to check if the water heater isn’t working.
• An On/Off switch that is accessed inside the WH panel on the outside of the RV. This powers the electric heating mode. It is OK to leave this in the ON position permanently AS LONG AS THERE IS WATER IN THE HOT WATER TANK… and I’ll show you why in a bit
• Thermostat that monitors the water temperature in the tank and closes the 110V circuit when the tank is not warm enough and opens the circuit once the water is hot enough.
• Electric Cut-Off (ECO) that is a fail safe mechanism for this system. If the thermostat fails to open the circuit and the water continues to heat up past 180 F, the ECO switch will be engaged and open the circuit and interrupts power to the system. There is a Reset button in the WH panel that can be used to close the circuit and restore power.  The Reset button on the left restarts the 12V electrical component of the propane heating system and the one on the right resets the electric heating system.

• If you take the plastic cover off the ECO Reset, you can take the voltage reading on the wiring terminals at the ECO (Hi-Limit) and the Thermostat to see if there circuit is broken.
• The electric element should be taken out and inspected. In our case, this was the culprit because it looked like this:

That there is a blown out element that happens if you have run the electric heating mode while the water tank was empty.

WE never did this but it would appear that the sellers had no water in the tanks (they plugged in to a hose) but they left the electric heating mode switched on the whole time which would have caused this to happen.

So kids, be very careful to never run your water tank empty if you are using electric heating mode.

Propane Heating Mode – Suburban Combo Water Heater (SW6DE)

I feel like I probably will write a much bigger post about the propane heating mode components because it is a little more complex but I can write a little bit about the basic components that helped us troubleshoot what was going on with our system. Here is the circuit diagram:

The propane heating mode uses 12 V electric power to power an electrode that is responsible for creating a spark to ignite the gas. There is a switch inside the camper which controls this mechanism. When the camper switch is turned on, you will hear a ticking sound and that is the control board purging air from the propane feed line and attempting to ignite through the spark. This will be done 3 times before it will lock out and you have to reset the camper switch for it to reattempt.

And like the electric heating mode, there is also a Fail safe ECO and thermostat that works in a similar fashion to prevent overheating.

Our problem was the propane heating would work fine for a while but then it would slowly fail to ignite and we would need to keep reseting the camper switch.

Finally, it just failed to light period. We would hear the ticking and the ignition sequence would end without actually lighting the propane.

A few things to check:

• AIRFLOW – A flame needs a good supply of oxygen. One of the first things we did was to open the WH panel and watch to see if it made a difference. If this fixes the problem, most likely, you’d want to check your vent and make sure it isn’t clogged up so the system isn’t starved of oxygen. When we tried this, the ignition sequence would fail a few times and then set off a mini explosion that was quite scary at night.
• Checking the gas valve and line – Without specialized equipment, we could rely on smell and sound to check that there was actually propane coming out of the valve. The fact that we saw a mini explosion meant most likely there *was* gas coming out but maybe the flow was not sufficient to ignite and maintain a flame indicates that a good next step would be to check that the piping wasn’t obstructed.

We proceeded to clean out the piping by flushing it out and reconnecting. That seemed to fix it for us! (Be sure to check that you have reconnected all the pipes without leaks)

CAVEAT: We are not qualified electricians or technicians and this is just a blog about our own DIY experience. If you are not comfortable doing your own RV repairs, hire someone who is!