Solar Hot Water Problems and What Each Symptom Means

Rheem's owner's guide for its Solar Loline, a split system with a pump and a controller, says that when the controller signals a problem, solar gain may not be happening and the booster ends up providing all of the hot water. When the solar side stops working like that, the taps may stay hot while running costs rise, so a higher electricity bill can be the only clue.

Usage patterns can do the same thing without any fault at all. Your Home, the Australian Government's guide to sustainable homes, notes that a household using most of its hot water in the morning may lean on the booster to reheat the tank before the sun has had a chance.

This guide concentrates on what heat does to a solar system, such as over-temperature, relief valve discharge on sunny days and boosters working with pre-warmed water, rather than frost damage. Each section says where an owner's checks stop.

On a pumped system such as Rheem's Loline, a series of red flashes on the controller may mean a fault, while a steady glow or rapid pulse can be normal operation. Split systems keep the tank on the ground and use a circulator, a small pump, to move water up to the roof collectors. Rheem's guide says the circulator switches on whenever the water in the collectors is hotter than the water in the tank.

On the Rheem Loline, the routine check is a green light that is on and a red light that is off. A green light that is off, or a red light flashing in a series, may mean the solar side is not working. Rheem's owner step is to switch the power outlet for the solar control unit off for a few seconds and back on; if the red light comes back, count the flashes and arrange an inspection. Other brands use other displays, so check the owner's guide for your model.

Your Home notes that pumped systems need more maintenance than thermosiphon systems, which have no pump at all.

A solar circulator running after dark is usually doing a job it was designed for, not failing. Rheem's guide for the Loline says the circulator can run at night under two operating modes, and that this is by design. Freeze protection moves tank water through the collectors when they approach freezing point. Night time cooling does the opposite job: after a day of strong sun or low hot water use, the system sends excess heat out through the collectors to bring the tank back down.

The same guide explains how the tank gets there. Once the tank reaches around 70 to 75 degrees, the circulator stops and the system enters over-temperature operation, while the collectors keep heating as long as the sun is up. A steady red glow on the controller during this stage shows heat building in the collectors, and Rheem says it is not a fault. After a sunny stretch with little hot water drawn off, a pump running in the evening is the system shedding heat.

A solar tank can run much hotter than a conventional heater, and on a hot day with little hot water drawn off, some relief valve discharge is expected. Solahart's owner's guide for its thermosiphon systems says the tank should reach 60 to 75 degrees in summer, and can reach around 90 degrees with high sun and low use. On a system without over temperature protection, Solahart describes heavy discharge from the temperature pressure relief valve in those conditions as the valve doing its job, says no service call is needed, and suggests an over temperature protection system can be considered.

Two exceptions matter. If heavy discharge happens while the electric booster is heating, Solahart says to switch the water heater off at the isolating switch or switchboard and arrange an inspection, by a licensed plumber or the manufacturer's service agent, who may need a licensed electrician for the booster controls. And outside hot, low-use spells, a small discharge during heating is normal, while more than a bucket in 24 hours points to another problem. Never climb onto the roof to reach the valve: relief valves are a job for a licensed plumber.

Water from a solar tank can be hot enough to scald, and Queensland controls the temperature delivered to taps on every new and replacement system. Business Queensland says stored hot water in a home must be heated to at least 60 degrees to prevent Legionella, and that a temperature control device, delivering hot water to taps at no more than 50 degrees, must be fitted to all new and replacement hot water systems. Solahart's guide warns that its tank temperatures can cause severe scalding, and that the water may be plumbed to fixtures such as the kitchen and laundry, where water hotter than 50 degrees is allowed.

So a kitchen tap that runs far hotter than the shower is not automatically a fault. Shower or bath water that suddenly runs much hotter than usual is different: stop using it and have a licensed plumber check the temperature control device. Changing the booster thermostat is not owner work either; Rheem's guide says a licensed electrical worker adjusts it.

When a solar system runs short, the booster is the first thing to check, because it covers whatever the sun does not. Rheem's checklist starts with the isolating switch and the circuit breaker marked hot water or water heater at the switchboard, plus any timer settings. If the booster is on an off-peak or time controlled supply, its heating hours are restricted, so water can be cooler in the morning when it has not run overnight. Where a timer is fitted, Rheem suggests an afternoon boost before evening use. Solahart's checklist adds shading, heavy use, leaks and whether the booster switch or time switch is on.

Weather plays a part too. Rheem notes that cloudy weather in the hotter months, or low sun in colder months, means the booster has to run more often. Heavy use is the other common cause: the same guide says people often do not realise how much hot water they use, particularly in the shower. If all of that checks out, the collector area may be too small, and Rheem says an additional collector is sometimes needed. A breaker that trips again after one reset needs a licensed electrician.

If the gas booster is a standard instantaneous unit not rated for solar preheating, it may shut down on warm afternoons because the sun has already heated the incoming water. Your Home explains that some instantaneous gas systems behave erratically at low flow rates when the incoming water is already warm, for example in warm climates or when pre-warmed by solar, because the burner cannot turn down far enough, so the unit shuts down for safety. Your Home adds that some units may not work well with solar preheating.

That is a compatibility question, not something to fix by adjusting the unit yourself. In Queensland, gas work covers installing, repairing, servicing and testing a gas system, and it needs a gas work licence. Before calling, note when the cut-outs happen, such as warm afternoons or low flow at one tap, and photograph the booster's data plate.

Less sun reaching the collectors means more work for the booster, and near the coast the glass has salt as well as dust to deal with. Rheem's guide says shade from trees or dirty collector glass greatly reduces how well the collectors work. Solahart asks owners to keep the glass free of dust and salt spray, and to wash it at least every three months if not enough rain has fallen; it says the glass can be hosed down. Do that from the ground, never from the roof.

A pumped system can also lose solar gain to air. Rheem's guide says air can become trapped in the collectors, for example after pipe work has been opened, and that this stops the circulator moving water around the collector circuit. The fix is for a plumber to purge the collector circuit of air, so a system that stopped contributing after recent plumbing work is worth mentioning when you call.

Cracked or shattered collector glass after hail or a falling branch is not an owner repair. Solahart's guide says no attempt should be made to remove or replace broken collector glass. Its warranty excludes glass breakage for any reason, including hail, and it suggests the collector glass be covered by home insurance, so check your policy before assuming the manufacturer will pay.

Keep people clear of any glass that has come down, photograph the damage from the ground, and have a licensed plumber assess the collector.

For a trip away, Rheem's guide for the Loline suggests switching the booster off to save energy, and says the power outlet to the solar control unit does not need to be switched off. Check your own owner's guide, because other models may differ.

Coming home after a long absence needs one safety step. Solahart's guide warns that if a water heater is unused for two weeks or more, flammable hydrogen gas can build up in the cylinder. It recommends running a sink hot tap for several minutes, with no smoking, open flames or electrical appliances running nearby, and not using a dishwasher or washing machine for this. Then switch the booster back on.

An owner's part ends at what can be seen and switched from the ground. Stop and call if the controller keeps showing a fault after one reset, a circuit breaker trips again, the relief valve runs heavily while the booster is heating, more than a bucket runs from it in a day outside a hot, low-use spell, shower water suddenly runs hotter than usual, collector glass is broken, or water is leaking from the tank or pipes.

In Queensland each part of a solar system has its own licence. Business Queensland says solar hot water systems must be installed by a hot water installer holding a QBCC solar and heat pump endorsement. The controller, pump wiring and booster element are electrical equipment, and the Electrical Safety Office says to always get a licensed electrician for any electrical work. A gas booster needs a person with a gas work licence. Before calling, photograph the controller's lights, the tank's data plate and any discharge.