How to replace a hot water heater

RV hot water systems (HWS) are not prone to failure as a rule but can eventually play up. The two most common RV HWS problems are heater anode failure and tank leaks.

Some systems have an anode that can be replaced if it fails. Others don’t, so the complete HWS unit must be replaced. If the boiler tank leaks the whole unit also must be replaced.

Most RV HWS can run on gas or 240-volt electricity (there are 240v/12v systems as well, although they don’t run too well on 12v).

Get the experts in

This brings us to the most important part of this job. Before you even think about replacing your HWS, be aware that you must have a licensed gas fitter check, test and certify your work (connecting the HWS gas line) and a licensed electrician to do the same on any 240-volt electrical work.

You’ll still save some money by doing the HWS replacement yourself, but make sure you factor in the inspection/testing required to say safe and legal.

Some HWS set-ups like this one here are plug and play – the 240v side of the system simply plugs into a nearby 240-volt socket – so there’s no wiring that needs to be certified by a licensed electrician. Most systems also run on gas though, and while it’s just a threaded connection you’re playing with, it’ll still need to be inspected and signed off.

While the HWS swap-over itself is fairly simple job, you will want to have adequate room and light to work, and have all the tools necessary and wear appropriate safety gear – such as solid footwear, for example. It also helps if you’re familiar with working with the tools required. If you’re not sure about any of this, leave it to the experts.

Long and short of it

Replacing a HWS can take not much more than an hour, or it can take many more. It depends on how much the HWS was built into the RV. RVs fit-outs are normally built with the floor and cabinetry installed first, then the external walls which can make the HWS hard to get to, and blow out the replacement time considerably just getting to the unit.

Fortunately, in the job shown here, the HWS was fitted to a shelf in an external storage compartment. Everything was easy to get at, with initial testing, the replacement itself and testing afterwards not taking much more than 1.5 hours.

In this case the condensation tube outlet had water pouring out of it; a good indication that the boiler tank was leaking.

Let's begin...

Start by turning off the gas at the bottle and disconnecting the gas line at the bottle. If the RV is connected to 240v power, switch off the power and remove the cord from the RV.

Now switch off the 240v power at the power pole and remove the HWS plug from the pole. Disconnect the gas line at the HWS and disconnect the 12v power connection.

With the water pump switched off, run some water at the kitchen or bathroom outlet to de-pressurise the water system.

Open the hot water drain to empty the HWS tank.

Then outside the van, remove the cowl over the HWS air inlet/exhaust (for gas operation) and remove the exhaust vent sealing frame.

Now the screws securing the HWS base to its mounting in the RV can be removed and the water inlet/outlet pipes (including the discharge pipe) disconnected. The water line connections use a sliding collar to ensure a positive connection so can be a bit tricky to disconnect.

The old HWS should now be free to slide out from its mounting position.

Fit the new hot water service into position, and plug in 12v control panel cable connector.

Fit 12v power and earth wires to the connector, and install the cover plate over the 12v electrics.

Seal the exhaust vent sealing frame with RV sealant and then screw down the exhaust vent sealing frame to the RV's body. Fit the cowl to the exhaust vent sealing frame.

Connect the water pipes and water discharge pipe.

To check that the new unit is operating properly, refit the gas connection at the gas cylinder and plug in the 240v socket (but don’t turn either on yet).

You should now get the gas connection tested, inspected and signed off by a licensed gas fitter.

Then turn on the water pump and fill the boiler and purge air out of the water lines (by turning on the hot water taps in bathroom and kitchen). When water comes out of the taps, the boiler is full. Now check the water connections at the boiler for leaks.

If that’s all good, turn on the gas at the gas cylinder and switch on HWS gas operation (at the switch usually fitted inside the RV).

Give the boiler about 10 minutes to heat up the water. Check to see if there’s hot air coming from the exhaust outlet – a good sign that the unit is working.

Try the hot water tap(s) after 10 minutes to see that the new HWS is functioning, being careful not to scald yourself with hot water. Now switch off the gas operation for the boiler.

To check 240v operation, give the system a while to cool down. Run water through the hot taps, making sure it has cooled down enough to test. Now flick the 240v switch on, wait 10 minutes and check the tap again (again, being careful not to scald yourself). You should have piping hot water.