Why is my hot tub not heating? (and how to fix it)

hot tub not heating

Help! My hot tub isn't heating...

Uh oh! Is your hot tub not heating?

You need your hot tub to be hot. Especially in Scotland. Where the thought of cooling off is only appealing during the two weeks of summer that we get.

So what do you do if your hot tub isn’t heating?

Don’t panic. There are a couple of things that could be causing this. And some of them have fairly simple and FREE fixes that you an do yourself. 

We go through some of the most common issues, that cause your hot tub to not heat. And how to fix them.

If you are unsure how to do any of these, please contact a specialist for help.

Common reasons your hot tub isn't heating (and how to fix them)

Step one, is to check for any error messages on your control panel. This could hint at what the problem may be.

If you are phoning a specialist to come out and fix the hot tub, then let them know about any error messages showing. This will help them to diagnose over the phone if possible. And will allow you to fix something that could be a minor issue. 

Or, if they still need to visit they may be more likely to bring the correct parts. 

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The most common problems that result in a hot tub not heating are:

1. Water flow or circulation problems.

2. Hot tub heating element fault.

3. Hot tub control board fault

1. Water flow or circulation problems

hot tub water flow

If your water is heating up very slowly. Or if your heating keeps turning off. You may have a flow problem. 

In this case, your control panel topside may show LF or FLO (or a similar flow message). 

This means there is an issue with water flow, and not enough water is passing through the heater. As a safety feature, the heater should be designed to cut out so it doesn’t burn out.

How to fix a hot tub water flow problem

There are a few possible solutions that you can try to fix your hot tub if you have a water flow or circulation problem. 

A few of them are very simple. And you can try them yourself before calling a specialist. Some of them you may need some help with. 

  1. Check water level
  2. Release any pump airlocks
  3. Clean your hot tub filter
  4. Check the pressure/flow switch
  5. Check the pump is working

1. Check the Water level

Firstly, and easiest. Check that you have enough water level in your hot tub. 

Hot tubs lose water through evaporation. And displacement (ie. if you jump in and water splashes out). You may need to top the water up if the level drops down too low. 

Otherwise, the hot tub skimmer will suck in air instead of water. This will cause the heater to cut out as not enough water is passing through it.

How to fix?


Just add some water. Exact water level varies, depending on the model. Check your manual if you are not sure.

2. Release any pump airlocks

If your hot tub isn’t heating, and you’ve recently emptied and filled your hot tub. Or if your water level was too low. You could have an air lock in the system. This means a bit of air is trapped, which is stopping water flow. And could mean little of no water is getting through the hot tub pipes and heater. 

To fix this, firstly:

  1. Fully open the jets (turn clockwise)
  2. Turn down, or disconnect the heater
  3. Turn on the jets and run for 10-15 seconds if water is coming out.
  4. Repeat until you see air bubbles coming out of the jets.

If you try this and water is not coming out the jets, but you hear the pumps trying to start, then you may have a more serious airlock. You will need to try and release this at source.In this case, do not try to run the pumps as it may damage them. You will need to:

1. Loosen off the union on the suction side of the pump till water starts coming out

2. Tighten the union back up (if you don’t your hot tub will leak)

If you’re not sure on how to fix this, then we recommend you contact a specialist. 

How to fix?


Release the air lock. Choose from the above options depending on experience and severity of air lock.

Either run the pumps and jets to flush out the air lock. Or loosen the union to release it at source.

3. Clean your filter

Coast Spas filter

If you have enough water, and there is no airlock then try to clean your filter. 

Your filter is responsible for catching all the dirt and debris. So the more you use it, the dirtier it going to get. If you don’t clean your filter regularly it can get clogged, and this can restrict flow. 

We recommend cleaning your filter monthly. And replacing every 6 months. 

Top tip: buy an extra filter when you get your hot tub. Then, when you are cleaning and drying one, you can pop the other in and keep using the hot tub.

A spare filter averages between £47 – £100 (depending on size). The larger the filter, the more expensive. But you will also have a larger surface area to catch dirt. 

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How to fix?


Clean the filter. Or if it's really clogged, you may have to replace it.

4. Check pressure/flow switch

After cleaning the filter, if you are still showing a flow fault, then it may be the pressure or the flow switch. The pressure switch is normally connected to the heater tube on a hot tub.

We would strongly recommend that you get a qualified electrician or hot tub technician to test this. As you are dealing with water and electricity. 

The best way to check this is using a multi-metre to check the continuity of the pressure switch.  

If this is faulty it will need replaced and usually costs approx. £40 + labour.

How to fix?


If there is a fault you will need to replace the pressure/flow switch in the hot tub.

5. Check the pump is working

Finally, if your hot tub is heating it could be that your pump is not working properly. This will mean that the water is not being pumped around the hot tub, which will restrict or stop the flow. Causing the heater to cut off. And your hot tub to get cold. 

If this is the case you will need to repair or replace the hot tub pump. 

How to fix?


Hopefully, you can repair the pump. However, it might be advisable to replace the entire pump to avoid future issues.

2. Hot tub heating element fault

If you’ve eliminated a flow fault. Then it might be something else. 

If there is power at the heater, but the water still isn’t heating, then it is likely a fault with the heating element. 

If this is the case, then again we strongly recommend that you get an electrician to check the heater element. as you will need to use a multi-metre to check the continuity.

How to fix?


Replace the heater element or the entire heater tube.

3. Control board fault

The control board in a hot tub is responsible for running everything including the pumps and heaters. If the other issues above are not responsible for the hot tub, not heating. Then it is possible that the control board is faulty, and either the P.C.B (printed circuit board) or the entire control board needs replaced.

This is usually a simple fix, but it’s one of the most expensive parts to replace and can be upwards of £1000 + VAT.

A problem sometimes occurs if you have an imported spa, without standard components. This can make it difficult or impossible to source and replace the parts. 

How to fix?


Hopefully, it's possible to replace the printed circuit board. If not

Other reasons your hot tub isn't heating...

hot tub hire

There are a few other things, that could result in you thinking there is a problem with the hot tub heater.

These probably aren’t anything to do with your hot tub heater. But may result in your hot tub not heating fast enough. Or your hot tub may lose heat.  

1. You’ve recently filled your hot tub

2. You have a poorly insulated cover

3. Got an air blower

1. Recently filled your hot tub?

On average your hot tub will take about 12-18 hours to heat up. This will vary depending on the heat that the water comes out the tap. So it will likely take longer in Winter. And less time in Summer. 

Give it time and if it’s still not heating see the above solutions.

2. Poorly insulated cover

Most of the hot tub heat is lost through the surface of the water. About 60% in fact. So to keep this in, you need a really well-insulated cover that is in good condition. Plus, you need foam insulation in the cabinet.

If you have a badly insulated cover you will lose heat quickly. This will reduce the temperature of your hot tub. Plus, your heater will work overtime to keep it at temperature. Resulting in sky-high hot tub running costs.

If your hot tub isn’t well insulated, get good a cover and add some cabinet insulation to keep your hot tub hot. And running costs down.

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3. Got an air blower on your hot tub?

Using an air blower is great, and adds a whole new dimension to the hot tub.
But, it will also draw in cold air, which can cool the hot tub down. Using it for 10-15 minutes shouldn’t be an issue. But just be aware that using it continuously can make the water feel cooler.

In summary

Hopefully, that has helped you understand why your hot tub is not heating. Sometimes, it’s a small fault. Easy to fix. Other times, you may need to get a part replaced.

If your hot tub isn’t heating. Check for any error messages. And, if you aren’t sure on what to do give an engineer a call, and give them as much information as possible on the fault. This way they can have an idea of what to bring and how to fix it when they arrive, which will keep your repair costs down.

If you have a problem with your hot tub give us a call. We offer servicing and repairs on all hot tub manufacturers.

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Debbie Ekins
Debbie Ekins
Eagle Leisure - Sales & Marketing Manager Mission = to arm you with the knowledge you need to make the best buying decisions. Fuelled by coffee (and naps). Explorer of Scotland and the world.