Solar Hot Water Repairs Adelaide: Boosters, Frost Valves and When the Tank Is Finished

Most solar hot water failures are not the collectors. The 3 parts behind the majority of callouts are the booster (an electric element and thermostat, or a gas booster), the tempering valve that mixes the outlet down to a safe temperature, and the frost and relief valves on the roof. All of those are repairable, and a booster repair is a modest job set against replacing the whole system. A leaking cylinder is the exception: that system is finished.

Related: Hot Water · Heat Pump Hot Water · Gas Fitting

The 3 faults behind most solar hot water callouts

Solar hot water systems fail in a predictable order, and the collectors are usually last on the list. Glass, copper and an absorber plate on a roof have very little to go wrong. What goes wrong is everything attached to them.

The booster. Every solar system has one, either an electric element and thermostat inside the cylinder or an in-line gas booster. A failed element, a dead thermostat, a tripped over-temperature cut-out, a booster switch somebody turned off, or a gas booster that will not light accounts for most no-hot-water calls.
The tempering valve. It mixes stored water down to a safe temperature at the tapware and it is a wear item. When it fails you either lose hot water at the tap while the tank behind it is full and hot, or you get dangerously hot water at the outlet.
The relief and frost valves. A temperature and pressure relief valve that has started passing, or a frost valve stuck part open, dumps hot water all day. The symptoms are a water bill that jumped for no clear reason and hot water that runs out early.

Flat plate or evacuated tube, roof tank or split

What your system can be repaired with comes down to 2 things: the collector type on the roof and where the cylinder sits.

Flat plate collectors: a glazed panel over a dark absorber. Robust, straightforward to replace, and they shed hail and debris well. They lose more heat to cold air, so their strength is summer and the middle of the day.
Evacuated tubes: rows of double-walled glass tubes with a vacuum between the walls. That vacuum is excellent insulation, so output holds up far better on a cold, still, overcast morning, which is why they earn their keep in the Hills. Tubes are individually replaceable, but they are glass on a roof and hail finds them.
Close-coupled: the cylinder sits on the roof above the collectors and circulates by thermosiphon, with no pump and few parts. A full cylinder is a serious load on a 1920s bungalow roof frame, and when it leaks you usually find out through the ceiling.
Split: the cylinder sits at ground level with a circulating pump, a controller and sensors at the roof and the tank. More to go wrong, all of it reachable, and the cylinder can be replaced without lifting anything onto a roof.

The difference shows up at repair time. On a split system a failed pump, controller or sensor is a parts job at ground level. On a close-coupled system with a leaking roof tank, the repair is a replacement, and moving cylinders over brittle Marseille tiles is a real part of the job rather than an afterthought.

Frost, glycol and the Adelaide Hills

Frost protection is the part of a solar system most owners have never heard of and the part that quietly causes the largest bills. Water sitting in a rooftop collector that freezes expands and splits the riser tubes, and the repair is a new collector.

Closed loop with glycol: the collector circuit carries a water and glycol mix that will not freeze, passing heat to the cylinder through a heat exchanger. Glycol degrades. Left long enough it turns acidic and corrodes the collector it was installed to protect, so it needs testing and changing on a cycle rather than being forgotten.
Frost valve: a temperature-sensitive valve at the collector that opens as it approaches freezing and bleeds warm water through the circuit. It works. A frost valve stuck open runs continuously, which shows up as constant dripping and a water bill nobody can account for.
Controller-driven circulation: the controller runs the pump to push warm tank water through the collectors when the roof sensor nears zero. It depends on that sensor and on the power staying on, which is why a blackout on a frosty Hills night is a genuine risk.

On the plains this is close to academic. Frost at Goodwood, Glenelg or Richmond is rare. Above the freeway it is not. Stirling, Aldgate, Upper Sturt and Mount Barker see frost most winters, and a system specified on plains assumptions, or one whose glycol has sat untested for a decade, is exposed every year it stays that way. If your system is in the Hills and nobody has checked the glycol or the frost valve, start there.

When the honest answer is not another solar system

Plenty of Adelaide solar hot water went onto roofs during the rebate years of the late 2000s and early 2010s, so a large cohort is reaching 15 years at once. When one of those cylinders fails the answer used to be another solar system. It is no longer automatic.

Collectors sound, cylinder failed, split system: replacing the cylinder and keeping the collectors is usually the best outcome. Have the collectors, sensors and glycol checked first.
Roof-mounted cylinder failed on a heritage or brittle-tiled roof: weigh removal, lifting a new tank and the tile damage that comes with both against a ground-level system.
Rooftop solar PV already on the house: a heat pump at ground level generally beats a new solar thermal system, because it runs on power you already generate and leaves the roof alone.
Collectors now shaded: if trees have grown over the roof since installation, a replacement inherits the same problem. That is a common and entirely avoidable mistake.

The honest position is that solar thermal remains an excellent system where it is already installed and the collectors are sound, and it is increasingly hard to justify as a brand new installation on a house that already has PV. We repair solar systems worth repairing, and we say plainly when a cylinder is finished rather than sell a repair that lasts a season.

Other hot water pages

Heat Pump Hot Water: Heat pump hot water supply, siting and repair across Adelaide. What the running cost really is, where the unit can sensibly go, and when a heat pump is not worth the change.
Rheem Hot Water Repairs: Repairs to Rheem electric storage, gas storage and continuous flow units across Adelaide, with a straight answer on when the cylinder is beyond saving.
Rinnai Hot Water Repairs: Diagnosis and repair of Rinnai Infinity continuous flow units across Adelaide. Fault codes read properly, gas and water sorted on the same visit by a licensed gas fitter.
Dux Hot Water Repairs: Repairs to Dux electric, gas, solar and heat pump hot water units across Adelaide. We read the compliance plate first, because on a Dux it settles the anode, warranty and parts questions at once.
Bosch Hot Water Repairs: Continuous flow gas repairs by a licensed gas fitter. Ignition faults, flow sensors, blocked inlet filters and hard-water scale on Bosch units across Adelaide.
Vulcan Hot Water Repairs: Gas storage repairs by a licensed gas fitter. Pilot lights that will not hold, tripped cut-outs, failed gas control valves and anode checks on Vulcan tanks across Adelaide.
Aquamax Hot Water Repairs: Electric storage diagnosis on Aquamax tanks across Adelaide. Elements, thermostats, cut-outs, relief and tempering valves, plus a straight answer on stainless tanks and anodes.

Questions we get asked

Why has my solar hot water gone cold?

On a run of cold or overcast days the collectors alone will not get the tank to temperature, and the booster is meant to cover the shortfall. When there is no hot water at all, the booster is the first suspect: a failed element, a dead thermostat, a tripped over-temperature cut-out, a switch turned off at the board, or a gas booster failing to ignite. The second suspect is the tempering valve, which can strand a full, hot tank behind a tap running lukewarm.

How long does a solar hot water system last in Adelaide?

Collectors commonly outlast the cylinder. Flat plate panels and evacuated tubes frequently run 20 years or more, while the storage cylinder typically manages 10 to 15 depending on water hardness and whether the sacrificial anode was ever checked. Boosters, tempering valves, pumps and controllers are shorter-life items and are expected to be replaced along the way. A system reaching 15 years is not automatically finished, but it is at the age where a repair needs to be weighed rather than assumed.

Is it worth repairing an old solar hot water system?

Usually yes, unless the cylinder itself is leaking. An element, thermostat, tempering valve, relief valve, pump, controller or sensor is a modest repair set against a whole new system, and it buys years rather than months. The 2 things that change the answer are a leaking tank, which cannot be repaired at all, and parts that are no longer manufactured for an obsolete model. We will tell you which of those you are dealing with before any work starts.

Can you replace just the evacuated tubes?

Yes. Tubes are individually replaceable, which is one of the real advantages of an evacuated tube array, and a hail strike that takes out 3 or 4 tubes does not condemn the collector. The limit is model support: tube diameters and lengths vary between manufacturers, and once a discontinued system can no longer be matched, replacement becomes the only path.

Why is water dripping off my roof from the solar unit?

Constant dripping from a rooftop solar system is almost always a valve. A frost valve stuck part open bleeds warm water through the collector all day, and a temperature and pressure relief valve that has begun passing does the same down the overflow. Both waste hot water and both show up on the water bill, so neither is worth leaving. On a roof-mounted cylinder, water appearing at the tank rather than a valve is a different and far more serious problem.

Should I replace solar hot water with a heat pump?

It is a strong option when the cylinder has failed, particularly on a house that already has rooftop PV or where the tank sits on the roof. A heat pump goes in at ground level, runs on power you already generate, and takes the load and the leak risk off the roof entirely. It is the wrong move where the collectors are sound and only the ground-level cylinder has failed, or where there is no outdoor position with real airflow away from bedroom windows.