Help! My Hot Tub is Not Heating

Hot Tub Not Heating

The last thing that you want when you have either just finished building your own DIY Hot Tub or you have just installed a brand new hot tub is that it doesn’t heat. Hopefully, this article will give you some insight of the kind of things to check for.


This blog and my YouTube Channel has lots and lots of information on Hot Tubs and Plunge Pools.

Hot Tub Not Heating – Check the Temperature Setting


The very first thing that you should check when your hot tub is not heating is that you have increased the set temperature on the topside control. Seems pretty obvious I am sure, however this is a must and in the haste to tun things on, people often forget this.


The topside control if you are not familiar with this term, is the keypad that has the buttons to control your jets. If you have not increased the temperature, then there might be the case that your thermostat is already at the set temperature so the heater in not clicking into play. Raise it up to 40C or 102F and see if you can hear the really click into play on the spa pack. On some topside controls there is also a heating indication light.


Hot Tub not heating – What Voltage are you running on?


This might seem an odd thing to say, but do check the voltage that you are running on. If you are running on a 110V system in the USA for example, do not expect your hot tub to be racing up to temperature in 30mins or an hour. This could be perceived as your hot tub is not heating.


It will take several hours for the water temperature to increase so it might just be a case that you have not waited long enough to see any results. Be patient. There is a limit on the heating capacity on 110V (due to the current draw) and it is usually less than 1.5KW in heat. On 220V then you can have up  5.5KW in a Spa Pack which will heat a lot quicker.


Ambient temperature and the insulation on the unit will also have an effect on heat up speed. So my point here is after you have checked things, be patient – it might take a couple of hours just to move the initial temperature.


Hot Tub Not Heating – Check the Spa Pack Setting


Some Spa Packs, especially ones from the USA can often have dual modes. By this, I mean that they can run at either 115V or 230V from your split system. I have more information on Hot Tub electrics in this post here.


However, my point for this one is that if you have a pack that is set to 110V and your electrical supply is 230V then you have a problem. You might get a circulation pump to run and it looks like things are ok, but your heater will not work as it will be expecting more electric and that could be why your hot tub is not heating.


Check for Flow Errors on the Spa Pack


Lights on and no one is home? Well, what I mean here in terms of the jets, is there any action on them. Can you see physical flow / water coming out of them. If not, is there an error code on the keypad that could indicate a flow error? If this is the case, the heater will not kick in.


There is a built-in safety mechanism to stop overheating in that when there is no flow, the heater will not turn on. That means if there is an air lock, which is quite possible after you have filled up, then there will be no flow and no heat.


Check the back of the circulation pump with your hand to see if you can feel the air from the pump. If you can’t see any action in the tub, then you most likely have an air lock. I have a post here on what to do.


Check for Flow Errors on your Heater / Air Source Heat Pumps


If you are not using electric and you have an external heating source like a propane heater or an air source heat pump, then they will have their own flow switches. Again, these flow switches are there to stop the units overheating.


If there is no water flow through the heater then the heater will not switch on – this could be why your hot tub is not heating. If there is too little flow through the heater then for safety, the unit will not switch on. Again, check for an air lock on these heaters, they are quite popular, especially after filling the tub up. Just loosen the union (screw nut) on the heater that is at the highest point on the heater and see if you can let any air out. This is the usual culprit.


Check the Fuse on the Spa Pack


The fuse for the heater could have blown. It is normally an easy one as it is one of the biggest two fuses on the Spa Pack. It does take quite a lot to blow the fuse for the heater so be careful. If you have an older hot tub, then the heating element could be bad and you might need to replace it. If you are on a new Spa Pack, then this could indicate a bigger problem.


Normally, on the inside of the Spa Pack, you will see a circuit diagram. Don’t worry if electrics is not your thing, you should still be able to read a fuse list. Take out the fuse that is labelled for the heater and replace it with a new one. Always worth a check before you have to pay for someone to come out and do the same.



If all else fails…


If all else fails, you need to be contacting the supplier of your plastic shell hot tub. If you have built your own, the I have probably helped you so please do get in touch with me and we will see what we can come up with.


I hope you have found this article useful.


Happy “hot” Tubbin’ (see what I did there lol)