fix tankless water heater

How to Fix the Most Common Tankless Water Heater Issues


A good tankless water heater should keep your water supply piping hot for around 20 years; this is great for guaranteeing a relaxing bath when you need it most! However, as with all products with mechanical components, tankless water heaters are prone to failure.

Let’s take a look at some of the most common problems you’ll experience and the steps needed to remedy them.

Water is Not Hot Enough

Providing cold water instead of hot is the ultimate failure for a tankless water heater, but occasionally this will happen. Whilst frustrating, the solution can often be as simple as:

  • Checking that the water temperature is adequately set; between 122 – 130F should be sufficient.
  • Identifying any ‘cross flow’ which is where cold water and hot water are mixing together e.g. through a leaking seal.
  • Double check that your gas supply line is capable of matching the gas line requirements for your system.

Investigating these potential problems should get you closer to getting that hot water supply back in no time.

Water is Too Hot

The only thing worse that water which isn’t hot enough is water which is too hot. I’m sure you’ve experienced that moment in the shower when it feels like molten lava is raining down on you; I know I have and the red skin it leaves isn’t pretty!

The best steps to take in this scenario are:

  • Check that the thermostat hasn’t been accidentally set or knocked too high – you’d be surprised how often this happens!
  • Identify whether the temperature sensor is damaged or has fallen out of position, you may be able to reposition this to reduce the temperature issue. If this doesn’t work, invest in a new one.
  • Look into whether you have a buildup of limescale (see below).

Low Water Flow

When there’s a drop in water pressure you’ll be faced with the disappointing sight of a dribbling water supply.

The most common cause of this problem is that there’s likely to be an obstruction within at least one section of the plumbing run.  I’d recommend that you investigate the following sections for an obstruction:

  • Water filter
  • Pipe run

Once you find the offending debris, this can be removed and you should discover that the water pressure should increase; that disappointing dribble of water will then return to its former, gushing glory.

Limescale Buildup

Limescale may look relatively harmless, but it’s actually one of the most harmful substances for your tankless water heater. A buildup of limescale can seriously reduce the efficiency of your tankless water heater and leads to an increase in burn cycle to compensate.

Naturally, this causes a lot more stress than your system needs and can reduce its lifespan considerably. And no one wants this!

If you live in a relatively soft water area then limescale shouldn’t be too much of a problem, but it will still build up over time. The best option in this scenario is to invest in a decent descaler solution which you will need to regularly flush through your system.

For those of you living in a hard water area then a regular descale is imperative as it will build up very quickly. To provide extra protection it’s also recommended that you invest in a water ionizer device which will prevent scale forming in the first place. These can be expensive and a decent one will cost upwards of $750, but the savings they provide in the long term are worth it.

Rusty Colored Water

Like me, you expect your water to be clear. Anything less than clear indicates a potential health hazard, so the sight of rusty colored water is bound to ring alarm bells.

The most common cause of rusty colored water in your system is due to a metal material called anode. When anode is regularly heated it begins to rust and, consequently, breaks down. Anode is mostly likely to dissolve in your pipework, so it’s essential that you look into getting this replaced immediately.

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