Troubleshooting Series – My Hot Tub Won’t Heat

If you’re having trouble with a cold spa, then read on to find out why this might be and what you should do.

Why Won’t My Hot Tub Water Heat?

This is a fairly common problem, and, in some cases is a pretty easy at-home fix. If your hot tub water won’t get warm, it’s most likely one of three things:

  1. Your hot tub is in the wrong mode.
  2. You have a blocked or low water flow, which you may be able to solve yourself by following a few simple steps.
  3. An issue with the heater, which will require a professional repair or replacement.

1. The Mode Needs Changing

The first thing to check is what mode your hot tub is in. If the hot tub is in economy or sleep/rest mode, then it will only heat during the filtration cycles. To check this, consult your owner manual. It’s likely that your panel will indicate that your hot tub is in rest or ready mode (ready mode being heating) with an LCD display, such as PMPS, PURG, AIR, SLP or similar, depending on the make and model of your hot tub. If you’re unsure, look up any display messages in your owner manual. A series of manuals can be found here, as well as a guide to common LCD messages/displays.

2. The Water Flow Is Blocked/Low

Your hot tub heater will need the right water flow to work properly, and if the flow is blocked for some reason it will shut down to stop the heater from getting damaged. Let’s take a look at the blocked water flow and how you can fix the problem to get your tub heating again. Here are some of the causes and what to do:

The Water Level Is Too Low

The first, and easiest, thing to check if your water isn’t heating is whether your water level is high enough. Too low, and your hot tub could be circulating a big dose of air into its systems, causing the heater to overload and switch off. If your water level is lower than the manufacturer recommends, be sure to top it up and reset your heater to see if this solves the problem.

The Filters Are Dirty

One of the most common causes of blocked water flow is dirty filters. If your water’s not heating, then it could mean your filters are clogged with dirt or debris, putting stress on the pumps and impacting water flow. Always be sure to clean your filters at least once a month for domestic use or weekly for holiday lets/heavy-use hot tubs, and replace them with new ones annually.

To clean your filters, switch off the power, take them out of the hot tub and soak them in a filter cleaning solution (according to the manufacturer’s instructions) to remove any oil and particles. Rinse them and allow to dry before putting them back. It’s best to always have two sets of filters so you can swap them while one set is drying. Once you have a clean set of filters in your hot tub, you can switch it back on and test to see if this has now solved the heater issue.

The Pipes Are Clogged

In a similar vein to the blocked filters, pipes that are obstructed by dirt or debris will also negatively impact water flow. Clean the lines using a product such as hot tub flush before draining and refilling your hot tub to see if this fixes the issue. Ideally, you should clean the pipes every time you drain and refill the hot tub (every 1-3 months, depending on usage).

There’s Air In the Pipes

If you’ve recently drained down and refilled your tub, then this could be the culprit. Incorrectly placing the hose during filling can cause the tub to fill before the pipes, leading to an airlock, and so interrupting the flow and shutting down the heater. If you think this might be the case, try removing the filters and turning on the jets for a few seconds to see if this clears out any airlocks. Don’t run for more than a few seconds as you don’t want to burn out the pump. If you’re unsure, call a professional.

The Pump Is Broken

If your pump doesn’t come on when you restart your hot tub, this could be the issue. In this case, you will need to contact your dealer to get a repair or replacement pump.

3. You Have a Heater Issue

If the heater itself is damaged, then unfortunately you can’t fix this yourself, and will need to call your dealer to book an appointment with a technician who can repair or replace the heater. Although you won’t be able to repair the issue yourself, there are steps you can take to help to prevent an issue in the first place.

Getting the Right pH Balance

If your pH is consistently too low, then this may corrode the heating element, causing it to break down the line. Be sure to check your hot tub’s TA and pH on a regular basis using a test strip. For more information on hot tub care and chemical balance, read our guide to hot tub maintenance.

Water hardness is also an important factor to check regularly. If the water is too hard, it can also create a calcium build up on the heating element; if it’s too soft, it can be corrosive, which can also damage the heating element, so be sure to test the water hardness regularly and adjust accordingly.

Remember, if in doubt, call your dealer. They can send someone to repair it, or may be able to talk you through some methods over the phone if the problem is a simple fix.

Hot Tub and Swim Spa Owner’s Manuals
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