If your solar hot water is slow to heat or only lukewarm, check the collectors on your roof first. Grime, salt, bird droppings or new shade stop them absorbing heat, so your booster has to do more of the work. That’s one of the most common reasons for slow heating, and a clean often fixes it.
But dirty panels rarely mean no hot water at all. If the water is completely cold, the cause is usually the booster, the power supply, a pump or the tank, and that’s a job for a licensed plumber or electrician. Here’s how to tell which you have.
First, rule out the obvious
- Weather and season. Solar hot water relies on sun. After several cloudy or rainy days, or in winter, it’s normal for the booster to do more of the work.
- Recent change in use. Visitors, a new baby or a bigger family can use hot water faster than the system heats it.
If neither fits, move on to the checks below.
What to check
1. Look at the collectors from the ground.
Check the roof panels or tubes for dirt, a salt haze, bird droppings, leaves or a new tree or structure shading them. See shade and solar panels for how shade affects output. Don’t climb onto the roof.
2. Check for visible damage.
Look for cracked glass, a collector with moisture or fog inside the glass, or tubes that look different from their neighbours. On many evacuated tube systems, a tube that has lost its vacuum turns from silver to white at the base. Damaged collectors or tubes need an installer.
3. Check the booster.
Most systems have an electric or gas booster that tops up the heat. If it isn’t working, hot water can run cold or lukewarm. For an electric booster, check your switchboard to see whether its circuit breaker has tripped. If it keeps tripping, or you smell gas, don’t keep trying. Call a licensed electrician or gas fitter, and call the gas emergency line if you smell gas.
4. Check the controller, if you have one.
Pumped systems have a controller, usually near the tank, with indicator lights or an error code. Note what it says and give it to your installer.
What it probably means
| What you notice | Likely cause | What to do |
|---|---|---|
| Heats slowly, booster runs a lot | Dirty or shaded collectors | Clean the collectors and check for shade |
| Only lukewarm on sunny days | Dirty or damaged collectors, or a circulation problem | Clean first. If it doesn’t improve, call an installer |
| No hot water at all | Booster, power, gas supply, thermostat or tank | Licensed plumber or electrician |
| Error light on the controller | Pump, sensor or controller fault | Installer |
| Leaking or dripping valve, unusual noises | Plumbing | Licensed plumber |
When cleaning helps, and when it doesn’t
A dirty collector absorbs less heat, so the system takes longer to heat the water and the booster runs more. A clean usually restores that, and you’ll see it in your energy bill or in how quickly the water heats.
It won’t fix a faulty booster, a failed pump or a damaged tube. If you’ve cleaned the collectors and nothing changes, the problem is somewhere else.
For a rough guide to when cleaning is due, see signs your solar panels need cleaning and how often to clean solar panels. Most Sunshine Coast systems need a clean every 6 to 12 months, and closer to 6 months near the beach.
What not to do
- Don’t pressure wash the collectors. High pressure can crack glass and damage seals. See can you pressure wash solar panels?
- Don’t climb onto the roof to check, especially if the glass is hot or wet.
- Don’t open the tank or touch valves. That’s plumber’s work.
- Don’t ignore a leak or a gas smell.
Get your collectors cleaned
We clean solar hot water panels and evacuated tubes across the Sunshine Coast, from Caloundra to Noosa, with a soft brush and purified water. Every clean includes a visual check for damage and a before-and-after photo report. If we see something that needs an installer, we’ll tell you.
See our solar hot water panel cleaning page, or get a free quote.
FAQs
Why is my solar hot water not heating?
The most common causes are dirty or shaded collectors, a booster that isn’t working, a power or gas problem, or a faulty pump or controller. Check the collectors and the booster first.
Can dirty solar panels cause no hot water?
Rarely. Dirty collectors usually mean slower heating and more booster use, not cold water. If you have no hot water at all, look at the booster, power supply or tank.
How often should I clean solar hot water panels?
Every 6 to 12 months for most homes, and closer to every 6 months near the coast.
Is it safe to clean solar hot water panels myself?
It involves working on a roof, and collectors can be hot and the glass fragile. Most people are better off with a professional. If you do clean them, avoid pressure washers and abrasive tools.
Who should I call if cleaning doesn’t fix it?
A licensed plumber, electrician or solar hot water installer, depending on the fault.