A Suburban on-demand water heater that won’t produce hot water doesn’t necessarily have a failed heater.

With the Suburban ST42 and ST60, some of the most common problems can come from things outside the water heater itself — particularly low water flow, insufficient propane supply, incorrect bypass-valve positions, or low 12-volt power.

And just like other RV tankless water heaters, water flow should be one of the first things you check.

The Suburban ST42/ST60 requires sufficient water flow before it will operate. Suburban specifies a minimum flow of approximately 0.7 gallons per minute.

If you’re camping somewhere with poor city-water pressure, the heater may therefore work perfectly well at one campground and refuse to ignite at another.

Before assuming the water heater has failed, work through the simple checks first.

Quick Summary

If your Suburban on-demand water heater isn’t working:

Check the error code on the control panel.
Make sure propane is available and turned on.
Verify that other propane appliances work.
Check your 12-volt power.
Open the hot-water faucet fully.
Check for restricted water flow.
Clean faucet aerators and shower heads.
Check the RV’s water-heater bypass valves.
If you’re on city water, try the fresh-water tank and RV water pump.
If the heater still won’t operate, use the error code to narrow the problem.

Don’t overlook water flow. It’s one of the simplest things to check and can look surprisingly similar to a water-heater failure.

Safety Stop

The Suburban on-demand water heater uses propane, electricity and a combustion system.

There are several checks an RV owner can safely perform, but gas-system and internal electrical repairs should be left to a qualified RV technician.

Stop troubleshooting and turn the heater off if:

You smell propane.
You see soot around the exhaust.
Wiring appears burned or melted.
The heater has been exposed to water internally.
The burner behaves abnormally.
You aren’t comfortable performing a particular test.

Never use an open flame to check for a propane leak.

Suburban also specifies that its gas appliances should be installed and serviced by qualified technicians. (Suburban RV)

Suburban ST42/ST60 Error Code Quick Reference

The control panel can considerably shorten your troubleshooting because the ST-series monitors several parts of its operating sequence.

Here are the codes identified in Suburban’s service documentation:

Error Code	What It Means	What to Check
E0	Outlet temperature sensor fault	Outlet temperature sensor or wiring
E1	Ignition failure	Propane supply, air in gas line, ignition/flame-sensing system
E2	Flame detected when it shouldn’t be	Flame-sensing/control problem — service recommended
E3	High-limit fault	Over-temperature/high-limit condition
E4	Inlet temperature sensor fault	Inlet temperature sensor or wiring
E5	Fan failure	Combustion fan or fan-speed signal
E6	Water over-temperature fault	Outlet water became too hot
E7	Gas-valve wiring fault	Gas-valve circuit/wiring — service recommended
E8	Pressure-switch failure	Combustion-air pressure switch or related circuit
E9*	Recirculation failure	Air in recirculation line / pump unable to prime
En	Water-heater timeout	Heater operated continuously too long
EC	Communication failure	Communication between controller and heater

*E9 relates to Suburban models equipped with the applicable recirculation system.

These codes tell you where the control system detected the problem. They don’t necessarily prove that the named component itself has failed.

For example, an ignition failure doesn’t automatically mean you need an igniter. The heater can’t ignite properly if it isn’t receiving the propane it needs.

Check First: Does the Heater Have Enough Water Flow?

This is one of my first checks with almost any on-demand RV water heater.

Suburban specifies that the ST42/ST60 needs at least 0.7 GPM of water flow for operation.

Turn a hot-water faucet fully on.

Then ask yourself:

Does the flow seem normal?

If the flow is weak, don’t start replacing water-heater parts yet.

Check:

Faucet aerators
Shower head
Water filters
Fresh-water tank level
RV water pump
City-water pressure
Kinked hoses
Plumbing restrictions
Water-heater bypass valves

A partially plugged faucet aerator can reduce flow much more than people realize.

Try More Than One Faucet

This is an easy diagnostic test.

If the heater starts normally from one faucet but doesn’t start from another, the water heater probably isn’t your primary problem.

Compare the flow.

If the bathroom sink activates the heater but the kitchen faucet doesn’t, check the kitchen aerator or plumbing for a restriction.

Try the RV Water Pump

This is one of my favorite tests when an on-demand heater won’t reliably ignite at a campground.

If you’re connected to city water and the pressure seems poor:

Fill the RV’s fresh-water tank.
Disconnect or shut off the city-water supply as appropriate.
Turn on the RV water pump.
Open a hot-water faucet.
See whether the Suburban heater now operates normally.

If it suddenly works, you’ve learned something important.

The water heater may be fine.

The campground’s water supply simply may not have been providing enough usable flow or pressure.

That’s particularly worth checking if the heater works at home or at one campground but acts up somewhere else.

Check the Water-Heater Bypass Valves

This one is especially important after winterizing or de-winterizing the RV.

Make sure the water-heater bypass valves are actually positioned for normal operation.

An incorrectly positioned bypass can interfere with water flow through the heater or allow cold water to mix into the hot-water plumbing.

Suburban specifically includes bypass-valve position among the checks for water-flow and ignition problems.

If the problem started immediately after the RV was de-winterized, I would move this check very high on the list.

Check the Propane Supply

If you have good water flow but the burner doesn’t ignite, check the propane supply.

Make sure:

The propane tank isn’t empty.
The tank valve is open.
The regulator is operating properly.
Other propane appliances operate normally.

Try lighting the RV stove.

If the stove also won’t operate properly, the Suburban water heater probably isn’t your first problem.

Did You Recently Run Out of Propane?

Air may be present in the propane line after the tank has been changed or the system has been shut down.

Suburban notes that initial startup can require several ignition attempts while air is purged from the gas line. The ST42/ST60 makes multiple ignition attempts before entering lockout.

Running another propane appliance can help establish that propane has reached the RV’s appliances.

Don’t repeatedly reset a heater indefinitely if it continues failing to ignite. If propane is available and the problem persists, further diagnosis may be required.

Check the 12-Volt Power

A propane-fired tankless water heater still needs electricity.

The Suburban uses 12-volt DC power for its control system, ignition, gas valve, blower and other components.

If the RV battery is extremely low or there’s a 12-volt supply problem, the heater may not operate normally.

Check whether other 12-volt equipment is behaving strangely.

If you have the equipment and experience to do so safely, verify the RV’s 12-volt supply.

Suburban’s service specifications list a nominal 12 VDC supply and an operating range of approximately 10.5–14 VDC for the ST42/ST60.

Suburban E1 Error — Ignition Failure

An E1 means the heater attempted ignition but failed to establish a flame.

Start with the simple things:

Is there propane?

Is the propane turned on?

Do other propane appliances work?

If the propane supply was recently interrupted, there may still be air in the line.

If the propane supply is good and E1 repeatedly returns, possible causes move farther into the ignition system, flame sensing, gas supply pressure or control system.

That’s where I’d start moving the diagnosis toward a qualified technician rather than recommending that an RV owner begin dismantling the burner system.

Suburban E3 Error — High-Limit Fault

An E3 indicates that the high-limit circuit has opened.

Don’t simply keep resetting the heater if this fault repeatedly returns.

A high-limit condition can be associated with excessive temperature or a problem within the safety/control system.

Check for obvious water-flow restrictions first.

If adequate flow is present and E3 returns, the heater should be properly diagnosed.

Suburban E5 Error — Fan Failure

The combustion blower has to operate correctly before the heater can safely ignite.

An E5 indicates that the controller isn’t receiving the expected fan-speed signal.

An RV owner can safely check the exterior vent for obvious obstructions, but internal blower, wiring and control diagnosis should generally be left to a technician.

Suburban E6 Error — Water Too Hot

An E6 indicates an over-temperature condition at the outlet water.

Check for anything that could be restricting water flow.

Reduced water flow through a tankless heater can affect its ability to control outlet temperature properly.

If flow appears normal and E6 repeatedly returns, stop resetting the heater and have the temperature-sensing and control systems checked.

Suburban E8 Error — Pressure Switch

The pressure switch is part of the heater’s combustion-air safety system.

An E8 indicates a problem involving the pressure-switch circuit or its expected position.

Before assuming the switch itself has failed, check the exterior vent for obvious blockage.

Do not bypass a pressure switch to make the heater operate.

It’s a safety device.

Suburban EC Error — Communication Failure

An EC code indicates a communication failure involving the heater’s controller.

Try turning the heater off and restarting it.

If EC immediately returns, the problem may involve the controller, communication wiring, connections or the main control system.

This isn’t the same as an ignition failure, so don’t start chasing propane problems solely because the heater isn’t firing.

Heater Starts but Then Shuts Off

This is another situation where I go back to water flow.

If the heater lights normally but repeatedly cycles on and off, watch what the water is doing.

Is the flow weak?

Does the RV water pump cycle at the same time?

Does changing the faucet position affect the heater?

Suburban’s troubleshooting information specifically identifies low water flow, restricted aerators or shower heads, pump operation, air in the plumbing and fluctuating source pressure as possible causes of rapid cycling.

Clean the aerators and shower head and make sure you have strong, consistent flow.

Hot Water Temperature Keeps Changing

Temperature fluctuations don’t automatically mean there’s a heater failure either.

Again, check the water supply.

Restrictions at faucet aerators, shower heads or strainers can interfere with operation.

If you’re on campground water, try your fresh-water tank and pump.

If the temperature becomes stable on the pump, campground water pressure or flow may be contributing to the problem.

Set the Temperature at the Control Panel

Here’s another trick that’s worth repeating from the general on-demand water-heater article.

Instead of setting the water heater extremely hot and then mixing a large amount of cold water into your shower, try setting the heater closer to the temperature you actually find comfortable.

Then use primarily hot water.

For example, once you determine a comfortable shower temperature, set the heater close to that temperature before showering.

This can help maintain stronger flow through the hot-water side of the system rather than throttling the hot flow down while adding cold water.

The ST42/ST60 control allows the outlet temperature to be adjusted, with a normal factory setting of 113°F and an adjustable range up to 131°F when its child lock is released.

Don’t Forget the Faucet Aerators

This deserves its own section because it’s such an easy thing to overlook.

If only one fixture has trouble producing hot water, remove and inspect its aerator.

Sediment and debris can restrict the aerator enough that an on-demand water heater doesn’t see sufficient flow.

This becomes particularly common after:

De-winterizing
Plumbing repairs
Changing filters
Filling from questionable water sources
Sediment entering the RV plumbing

A five-minute aerator cleaning can sometimes fix what looks like a failed $600 water heater.

When to Book Service

Call a qualified RV technician if:

You smell propane.
Soot appears around the exhaust.
E1 continues despite a confirmed propane supply.
E2 repeatedly appears.
E3/high-limit faults return.
E5 fan faults continue.
E6 over-temperature faults continue.
E7 gas-valve wiring faults appear.
E8 pressure-switch faults persist.
EC communication faults won’t clear.
The heater has good water flow, propane and 12-volt power but still won’t operate.
You’re uncomfortable working around propane or electrical systems.

Don’t bypass safety switches or modify the gas system to force the heater to run.

Service Call Prep

Before booking service, write down:

Your exact Suburban model number
The displayed error code
Whether the burner attempts to ignite
Whether you hear the combustion fan
Whether other propane appliances work
Whether the problem occurs at every faucet
Whether water flow seems strong
Whether the heater works using the RV pump
Whether it fails only on city water
Whether the RV was recently winterized or de-winterized
Whether the propane supply recently ran empty

Those details can dramatically shorten the diagnostic process.

Why Water Flow Matters So Much

A traditional tank water heater stores hot water.

An on-demand heater doesn’t.

It has to recognize water movement, begin its operating sequence, ignite the burner and regulate the burner output while water is flowing.

That’s why something as simple as a clogged faucet aerator or weak campground water supply can cause symptoms that seem completely unrelated to plumbing.

If your Suburban on-demand water heater isn’t working, don’t start with the expensive parts.

Start with:

Water. Propane. 12 volts.

Then let the error code tell you where to go next.

Frequently Asked Questions

Why won’t my Suburban tankless water heater ignite?

Start by checking water flow, propane supply and 12-volt power. The ST42/ST60 requires sufficient flow before beginning normal operation.

What does E1 mean on a Suburban tankless water heater?

E1 indicates an ignition failure. Check the propane supply first, particularly if the RV recently ran out of propane. Persistent E1 faults may require diagnosis of the ignition, flame-sensing or gas system.

Why does my Suburban water heater work at some campgrounds but not others?

Water pressure and flow can vary significantly between campgrounds. If flow becomes too low, the heater may not reliably activate.

Try filling the fresh-water tank and using the RV’s water pump. If the heater works normally, the campground supply is a strong suspect.

Why does my Suburban heater work at one faucet but not another?

Check the aerator or shower head at the problem fixture. A restriction can reduce flow enough to interfere with heater operation.

Why does my Suburban on-demand heater keep turning on and off?

Check for low or fluctuating water flow, plugged aerators, shower-head restrictions, pump cycling and poor city-water pressure. These are specifically included in Suburban’s troubleshooting guidance.

Can I reset a Suburban on-demand water heater?

Some lockouts can be reset by turning the faucet off and back on or cycling the heater off and on. However, don’t repeatedly reset a recurring safety fault without finding its cause.

Should I mix cold water with an on-demand water heater?

You can, but I often prefer setting the water-heater temperature closer to the temperature you actually want at the fixture. That allows you to maintain better hot-water flow, which can be particularly helpful when diagnosing marginal-flow problems.

Written by Dan Harvickson (Founder of Last Mountain Tech) RV Specialist

Suburban On-Demand RV Water Heater Troubleshooting: Error Codes & What to Check