Why Is My Geyser Making Noise? (Popping, Knocking & Hissing Explained)

Geysers are supposed to be almost silent. If yours is suddenly popping like popcorn, knocking when you open a tap, or hissing in the roof, it is telling you something. Some sounds are harmless. Others mean you are weeks away from a burst geyser and a ruined ceiling.

Here is what each noise actually means in a South African home.

1. Popping or crackling (like popcorn)

Cause: Scale and sediment have settled at the bottom of the tank and on the element. Water trapped under the layer flashes to steam and "pops" out.

Risk: Medium. It is wearing the element out fast and pushing your electricity bill up.

Fix: Drain and flush the tank. If the popping continues, the element needs replacing , see how long a geyser element lasts.

Cost: R900-R1,800 for a drain + flush. R1,500-R3,000 if the element goes too.

2. Knocking or banging when you open or close a tap ("water hammer")

Cause: Pipes are not properly clipped, or pressure is too high, so water slamming to a stop shakes the pipes against the trusses or wall.

Risk: High over time , it loosens fittings, cracks solder joints and can eventually rupture flexi-hoses.

Fix: Plumber installs a water hammer arrestor or re-clips loose pipes. Often also drops the incoming pressure with a PRV (pressure reducing valve).

Cost: R600-R2,500 depending on access and how many points need arrestors.

3. Hissing or whistling in the roof

Cause: Usually one of three things:

1. The pressure relief valve (PRV) is slowly releasing , normal in small bursts after heating, but constant hissing is a fault.
2. A pinhole leak on the geyser or a copper pipe, with water flashing to steam.
3. The vacuum breaker is faulty.

Risk: High , constant PRV discharge usually means the valve is failing OR the incoming pressure is too high. Either way you are heading for a burst.

Fix: Replace the PRV and check static pressure. If pressure is over 600 kPa, fit a pressure regulator.

Cost: R800-R2,200 for a PRV swap + pressure check.

4. Humming or low buzz

Cause: A loose element vibrating against scale, or a thermostat issue.

Risk: Low to medium , annoying but not dangerous on its own. Often the element is on its way out.

Fix: Tighten or replace the element.

Cost: R1,500-R2,800.

5. Rumbling or boiling sound

Cause: Thermostat is stuck or set too high (over 75°C), so the water is genuinely starting to boil inside the tank.

Risk: Urgent. A boiling geyser with a faulty PRV is how ceilings come down. If your thermostat is stuck at full heat, the geyser can over-pressurise.

Fix: Switch the geyser off at the DB board immediately and call a plumber today. Replace thermostat, test PRV, drop the setpoint to 60°C. See what temperature your geyser should be set to.

Cost: R1,200-R2,500.

6. Dripping or trickling sound (but no visible leak)

Cause: Water is running out the overflow pipe outside, usually because:

• The PRV is leaking
• The geyser is overfilling
• Or there is an internal leak you cannot see yet

Fix: Walk outside and check the geyser overflow pipe. If it is constantly dripping, call a plumber , this is often the first sign of a burst geyser within weeks.

When to switch the geyser off NOW

Flip the geyser breaker off at the DB board and call a plumber the same day if you hear any of these:

• Loud rumbling or boiling
• Constant hissing from the roof
• Steam coming out of the overflow
• Knocking combined with a wet patch on the ceiling

These are the noises that come right before a burst geyser. Insurance will pay for the geyser, but most policies will not cover the water damage if you ignored obvious warning signs.

Bottom line

A quiet ticking as the geyser heats and cools is normal. Anything louder than that is the geyser asking for attention. Catch it early and you pay R1,500. Ignore it and you pay R25,000 for a new ceiling, carpets and a geyser.

Find a vetted plumber near you before the small noise becomes a big claim.