A lot of the calls we take about a dead hot water system turn out to be a part. The tank is fine, the plumbing is fine, and something inside the unit has failed in a way that takes about an hour to put right.
So before you start pricing a replacement, it is worth knowing what the symptoms actually point to.
Is it the tank, or is it a part?
One quick test. Look at the base of the unit and the wall behind it.
If there is water pooling underneath, a rust stain running down the casing, or a damp patch on the wall, the tank has probably split. Once a tank is leaking it cannot be repaired and the unit has to be replaced — there is more on that in what a new hot water system really costs.
If it is dry under there and the water has simply gone cold, keep reading. Dry and cold is a part.
The hot water runs cold, or only ever gets warm
This is the most common one by a wide margin, and it is one of three things:
- A faulty element. The element is what heats the water. When it fails, the tank fills with cold water and stays that way. It is the usual culprit when the hot water disappeared all at once rather than gradually.
- A faulty thermostat. The thermostat tells the element when to work. A failed one can leave you with no heating at all, or with water that is warm but never properly hot.
- A faulty tempering valve. The tempering valve limits the temperature at the tap to 50 °C. When it fails it can fail in the direction of "too cold", so the tank is doing its job and the valve is throttling it on the way out.
Telling those three apart is a meter test, not a guess, which is the part worth paying someone to do rather than buying parts and hoping.
There is hot water, but no pressure
Different problem, different list:
- A faulty duo valve, pressure limiting valve or tempering valve
- Debris blocking the pipework or the valves themselves
Debris is more common than people expect, particularly after any mains work in the street. If the cold pressure is fine and only the hot side has dropped, the restriction is on the hot side — which narrows it down considerably.
The hot taps hammer or bang
Water hammer from the hot taps is usually:
- Faulty valves, or debris sitting in the valves
- Loose hot supply pipes — the banging is literally pipe hitting timber
- Worn tap washers
The last one is worth noting because it is the cheapest possible explanation and it is frequently the right one. A tap that has started hammering has often just worn its washer out. See what a tap service involves.
What each repair costs
| Repair | Price | |---|---| | Replace heating element | $185 | | Change thermostat | $195 | | Replace 15 mm duo valve | $138 | | Change pressure limiting valve | $179 | | Tempering valve, with new insulation kit | $199 |
All prices are GST inclusive and subject to site inspection.
Worth putting those next to the alternative: a replacement system installed starts at several hundred dollars more than any single repair on that list. If a plumber looks at a fifteen-year-old tank that is dry underneath and immediately quotes you a new unit, it is fair to ask what they tested.
When a repair is the wrong call
We will say so when it is. If the tank is already leaking, a repair is money spent on a unit that is going to be replaced within weeks. If the unit is close to twenty years old and the element has gone, you can absolutely replace the element — but you should know you are likely to be having this conversation again, and the valves will need doing then anyway.
The deciding question is usually: is the tank sound? If yes, repair it. If no, replace it.
Before you call
Two things that get the right parts onto the van the first time:
- The brand and capacity. Both are on a sticker on the front of the unit.
- What it is doing. "Cold from every hot tap since yesterday" and "warm but never hot for a month" point at different parts.
Then call us on the number at the top of the page. Many problems with electric hot water systems can be repaired within the hour, and we would rather do that than sell you a tank you do not need.
More detail on hot water systems.
More on Hot water systems, including what we charge.