Hot Water Tank Not Heating? Here’s Why

If your hot water tank is not heating, you’re likely frustrated. Luckily, those of us at DreamyHome have dealt with this issue more than we’d like to admit. We’re going to discuss the most common issues with hot water heaters and how to fix them, so keep reading! We’ll have your water toasty and perfect in no time.

The most common causes of a hot water tank not heating are the thermostat, TRV, pilot light, electric ignition system, water pressure, damaged or loose parts, or a lack of power.

Those are a lot of potential problems. Let’s break them down a bit more, shall we?

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Top 7 Causes of a Hot Water Tank Not Heating

There’s no way to just look at your hot water heater and know what’s wrong. This is, unfortunately, be a troubleshooting process that may take a bit, so buckle in. We’ll start with the easy checks and move on as things get more intensive, so be sure to go through the list in order – you’ll thank me later.

Lack of Power

The first thing you should always check with electronics is their power supply. That rule applies doubly to your boiler, as it’s a major part of your home. so first things first, let’s go take a look at the main circuit breaker.

Assuming no breakers are flipped, and all of the fuses are intact, check out your plugin. Is the cord damaged, frayed, or even unplugged? If it’s unplugged, fix it, and if it’s damaged, you’ll need to replace the cord.

Other potential issues include a lack of gas if it’s a gas-powered heater, and an internal safety switch being flipped in the heater. These are generally located near the base of the heater or wired into the thermostat.

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Temperature and Pressure Release Valve (TPR)

We’re going to talk about this more below, so this will be a brief section. The TPR valve of your water heater is a vital safety measure designed to prevent catastrophic failure (boiler explosions). You cannot cap off the TPR, as this will allow the pressure and temperatures to rise relatively unchecked.

Annually test your TPR and water heater to ensure they’re both in working order. If the TPR leaks, do what we detail below and then call a professional. This is, like I said, a safety measure that prevents very bad things from happening. If it fails, you run the risk of a literal boiler explosion in your home – that is, in case you’re not aware, a very bad thing to happen.

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Loss of Water Pressure

If you’re unsure how to repressurise a boiler (or check their pressure) check out our article here! It will walk you through the process and give a few tips to keep things running properly. These include bleeding radiators (if you have them) and restarting the boiler, so be prepared for a bit of work.

Assuming you’ve tried all of the steps mentioned in that article already, it’s time to move on to the TPR valve. This is the valve that opens when the water temperature or pressure rises too much as a safety measure (we just talked about it). A significant, sudden change in pressure or temperature can force the TPR to remain open, which will lead to issues with water pressure later down the line.

If you’ve noticed your TPR valve leaking or opening regularly, you can lower the temperature on your thermostat (attached to the boiler, not your home thermostat). This will reduce the pressure and temperature needed, and ease the workload of the valve. Place a bucket under the valve and open the handle to flush it, and then call for help. These are both temporary, stop-gap measures. They will not permanently solve the issue, but delay it from getting worse.

Beyond installing an expansion tank (expensive and not ideal) there’s not much you can do here. Really, the only option is to call in a professional to take a look. They may need to replace your TPR valve, or make other repairs – but something is likely wrong internally.

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Loose or Faulty Parts

This is one of those things where the issue may be super small and easily fixed, or a major task to perform. Begin by taking a look at the piping running from your water heater. If you notice leaks at various nuts and bolts that join pipes, you can tighten them manually. Should this solve the leak and water pressure, then all should be well.

If you either can’t tighten the bolts, or you did and it didn’t solve the issue, you’re going to need to call a professional. This is especially important if the leak is in the bottom of the boiler, as that means you either have a blown gasket or a leak in the tank itself. Neither of these is something a layman should perform – you’re working with electricity and water, which is a dangerous combination. Let the professionals do their job and don’t try to fix things beyond your means.

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Electronic Ignition

An electronic gas-ignition system is, generally, very safe. It uses a solid-state circuit to control flame ignition and keep it going. Should it go out, it’s likely due to a clog which can be cleaned. Keep in mind that if this doesn’t work, you’ll likely need a replacement installed by a professional.

To clean an electronic ignition system for your water heater, do the following:

  1. Turn off your heater at the breaker.
  2. Remove the panel in from of your burner, usually these are on the front.
  3. Pull the flame sensor from the heater.
  4. Wipe it with fine-grit sandpaper, getting everything you can off of it. Do not use anything that is flammable to clean the igniter (like rubbing alcohol).
    1. If there is a buildup inside the igniter, you can carefully use a paperclip or similar item to knock it loose.
  5. Reinstall and test the igniter after turning the power back on. If it doesn’t work, call a Gas Safe engineer to help find and fix the issue.

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Pilot Light

The pilot light for your gas water heater uses a thermocouple or thermopile to safely remain lit. It uses an electric current to keep the flame running, and if it goes out, a gas valve closes to prevent a leak.

First and foremost – if you notice a gas leak after your pilot light has gone out, do not relight it. Turn off the gas in your home, turn off the heater, and open some windows. Air out your home and call a professional to inspect your heater. Gas leaks are extremely dangerous and not to be trifled with.

If your pilot light keeps going out, it’s likely due to one of a few causes:

  1. The valve is defective and needs replacement
  2. A draft is blowing out the flame
  3. Corrosion has closed off your igniter. This is especially common in damp areas (like a basement, where most water heaters rest)


This is a slightly more difficult issue to pinpoint. If you have a single-element heater and your thermostat goes out, you’ll have no hot water. In a two-element heater, you may have two thermostats, making troubleshooting a bit more difficult. You may have hot water still, but it will be less hot and not as readily available.

Reset your thermostats (there’s usually a reset button or “high-limit switch”). If this doesn’t solve the issue, it’s likely that the thermostat(s) need to be replaced. Call a Gas Safe engineer to ensure this is the issue before replacing. Nobody wants to waste money replacing parts that don’t actually need it.

Final Thoughts

Troubleshooting a hot water tank can be a pain. They’re complicated machines with a lot of parts, and if even a single part goes out, the whole thing can fail. While there are a few things to check that we mentioned above, it’s more likely than not that you won’t be able to solve the issue alone. Try the tips we gave above, and then admit defeat if needed.

Call a Gas Safe engineer, make a drink, and sit back while the professionals do what they do best.

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