Solar heater faults and how to fix them

Most of the solar heater faults we see on inspections aren't manufacturing defects — they're one of three simple situations: weak heating from dust buildup or new shade, water that isn't hot enough because of a capacity mismatch or a backup-element issue, or a leak at a connection. A technician who's seen hundreds of cases can usually tell them apart with two questions. This article walks through each symptom, its likely cause, and what a technician actually checks — so you can diagnose the basics yourself before you call.

Problem one: the water isn't hot enough

The first question any technician asks is: "does this happen all the time, or only on certain days?" The answer changes everything.

• If it's winter or cloudy days: this is completely normal — output drops with less sunlight, and that's exactly the situation the backup element is there for. The first thing to check is whether the backup element is actually working. If this happens every winter, the full explanation and how to handle it is in Does a solar heater work in winter?.
• If it's happening all the time, not seasonally: the most likely cause is a capacity smaller than your household actually needs — especially if the family grew since the heater was bought. The second possibility is new shade that's appeared on the roof (a neighboring building went up, or a tank got placed nearby) that wasn't there at installation.
• What the technician checks: panel cleanliness first, since it's the quickest thing to rule out, then shade on the roof, then how current capacity compares to household size.

Problem two: heating gets gradually weaker over time

The telltale sign here is that performance was fine at first and has been slipping gradually over months, not suddenly. The single most common cause, by far, is dust buildup on the panels — even a thin layer noticeably cuts sun absorption, and it accumulates faster near busy roads or during windy seasons. The fix is usually simple and doesn't need a technician: periodic panel cleaning. If cleaning doesn't fix it, we look at other causes like the panel angle itself or an internal connection issue.

Problem three: a water leak

This is different from the two above — it's not something to wait out or fix yourself. The first thing a technician looks at is exactly where the leak is: from a visible joint, it might be a simple seal fix; from the tank itself or insulation under the roof, it's more involved and could relate to insulation age or excess pressure in the system. That's why the safety valve (which automatically releases any pressure buildup) gets checked as part of any leak inspection — sometimes the leak itself is a symptom of abnormal pressure, not just a loose joint. A leak always needs a technician — putting it off affects the roof itself, not just the heater's efficiency.

When do you actually need a specialist?

Simple rule: periodic panel cleaning you can safely do yourself. Anything else — a leak, electrical issues with the backup element, or persistent weak heating after cleaning and ruling out shade — needs a technician's check. Our after-installation follow-up is available through periodic maintenance for scheduled checks, and emergency maintenance if the problem needs a quick response. If your heater is still under warranty, make sure its status is registered through warranty activation before any outside intervention, so the warranty isn't affected.

Faults tied to water quality or the season

Some issues aren't about the heater at all — they're external conditions. High water hardness in some areas speeds up how fast the magnesium anode inside the tank gets used up, which means it needs checking more often than usual. And in winter, it's completely normal for overall performance to drop compared to summer — that's not a fault, it's expected solar behavior, and how to handle it properly is covered in Does a solar heater work in winter?. A technician can usually tell a real fault apart from normal seasonal behavior from a short description alone.

Does the original installation quality affect later faults?

Honestly, yes, quite a lot. A large share of the recurring leaks and faults we see trace back to a rushed initial installation — a connection that wasn't sealed tightly enough, or a panel orientation off enough that the backup element ends up working harder than it should and wears out faster. If you're about to install a new heater, the full correct-installation steps are in Installing and maintaining a solar water heater, and a practical tip: pick a company with a trustworthy installation track record from the start rather than fixing faults later — details in How to choose a reliable heater installer.

Quick questions a technician asks before diagnosing anything

To save time on the call, have answers ready for these: did the fault appear suddenly or gradually? Does it happen all day or at a specific time? When were the panels last cleaned? And has anything changed around the heater recently (new construction, a new tank, piping work)? These answers cut diagnosis time significantly, and sometimes clarify the cause without needing a site visit at all.

Book a free inspection or get in touch directly if you have a fault that needs an immediate check.