Unit is Running But Not Heating
Hello. We're sorry you're experiencing a heating issue with your control unit — this guide will help you get it sorted.
Before you start
The yellow cord reset below will not resolve an error code on your display. If your unit is showing an error (e.g. E1 or F1), see our E1 and F1 Errors guide instead. This reset is only for a unit that is running but not heating, or losing heat.
How to reset the heater
- Turn power off to the unit — either at your PRCD on the control box cord (press the test function) or by switching off power to your unit at the wall.
- Go to the heating unit and slide your hand underneath. Locate the yellow reset cord and pull it gently until it stops. You should hear a faint click, confirming the heater has been reset.
Here's a short video showing the yellow cord heater reset.
⚠ Warning
Pulling the cord too hard will force the reset arm off its hinge, and it will not reset the heater.
- Turn the switch at the wall back on and/or go to the PRCD on the control box cord and press reset to turn your spa back on. Press test to confirm it turns off, then press reset again. Operate the spa as normal — you should see the temperature climb roughly 1°C – 1.5°C per hour.
Why this happens
If the heater needs resetting, the internal temperature has reached 45°C. When this happens, the heater disengages itself from the active circuit to protect the system — the panel or Smart Control display will look normal, but no power is reaching the heater.
The most common cause is dirty or old filters (over 6 weeks old), which restrict flow through the heater and let its internal temperature climb too high. See our Filter Cleaning and Replacement guide to keep this from recurring.
A water level below the inlet grill, or people splashing in the pool, can also cause the system to draw in air — which has the same effect on internal temperature and trips the same high-limit reset.
If your spa is brand new and not heating out of the box, this reset will most likely fix it — the high limit can activate during shipping simply from movement and vibration in transit.
If the reset won't pull
If you think you've accidentally pulled the reset cord too hard and the heater won't reset, you can check the reset arm:
- For all Frame series spas (Oslo, Denver, Rova), see the video here. Note: a non-Frame control unit is used in the demo, but the process is the same.
- For all other models (internal control unit), you'll first need to remove the control unit from the spa shell, as shown below.
⚠ Handle the white rotation knob with care
After removing the retaining screw, gently pull the knob outward while slowly turning it — it will ease out. When re-fitting it, gently push inward while rotating; you'll feel it lock into place, then tighten the screw.
There is a very thin microswitch directly underneath the knob's socket. Forcing the knob in or out can damage this microswitch, which will stop the bubbler working and require a replacement part.
If the heater reset keeps popping and your filters are clean and/or new, it's possible there's limescale build-up in the heater — this happens when pH runs too high. Test your water weekly and adjust pH as needed to stay in range. See our Limescale Prevention and Treatment guide for the full fix.
Still not resolved?
If none of the above corrects the problem, or the reset keeps popping, you'll need to send your control unit only to our technical team in Christchurch to assess. Please:
- Send just the control unit to the address on the Return Control Unit Form below.
- Include the form with your details and Shopify order number (if known) inside the box — a banana box works great for shipping.
- Do not include inlet/outlet grills or rotation knobs with your control unit.
It's not necessary to contact us before sending your unit, provided the form is included in the box.
👉 See our new cost-saving prepaid return shipping policy here.
