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Hot Tub Not Heating Up? Here's What to Check

A hot tub that won't heat is the single most common problem we see across Bournemouth, Poole and Christchurch — especially in spring when tubs come out of winter storage. The good news: about 60% of heating failures have a simple cause you can check yourself before calling an engineer.

This guide covers all brands — Lay-Z-Spa, Intex PureSpa, MSPA, CleverSpa and hardshell hot tubs. We'll start with the easy fixes and work through to faults that need a professional.

Quick Checks First (5 Minutes)

Before you assume the worst, rule these out:

1. Is the Filter Blocked or Collapsed?

This is the #1 cause of hot tubs not heating — and the easiest to fix. Remove the filter cartridge and inspect it:

• Dirty/discoloured filter — Rinse thoroughly under a tap, or replace if it's been in use more than 2 weeks without cleaning
• Collapsed or deformed filter — Common with cheap replacement cartridges. The filter material sags and blocks water flow. Replace with an OEM or quality aftermarket one
• No filter installed — Some people remove the filter and forget. The pump needs the filter housing in place to maintain proper flow

On Lay-Z-Spa models specifically, a dirty filter is the most common trigger for E02 error codes which will also stop heating.

2. Is the Water Level High Enough?

Check the water is above the minimum fill line marked on your tub. Low water means the pump can't circulate properly, which triggers safety cutoffs that prevent heating. This is especially common after:

• Splashing (kids, vigorous use)
• Evaporation over several days
• A slow leak you haven't noticed yet

3. Are the Hoses Kinked?

On inflatable hot tubs (Lay-Z-Spa, Intex), the hoses connecting the pump to the tub can get kinked or pinched — especially if the tub has been moved or bumped. Straighten them out and make sure there's no restriction.

4. Power Cycle the Pump

The classic "turn it off and on again." Unplug the pump from the mains, wait 30 seconds, plug it back in. This resets any temporary sensor errors and clears fault states. It works more often than you'd expect.

Check for Error Codes

If your hot tub has a digital display, look for an error code. These tell you exactly what's wrong:

• E02 — Water flow/temperature sensor fault (most common)
• E06 — Heater relay or triac failure
• E03 — Overheat protection triggered (thermostat)
• E04 — Thermal cut-out / dry-run protection
• E08 — PCB communication error

See our complete error code guide →

If there's no error code but the heating icon is showing and the water isn't getting warmer, that points to a different set of issues.

No Error Code But Still Not Heating

This is the trickier scenario. The pump thinks it's heating but the water temperature doesn't rise. Possible causes:

Faulty Heater Element

The heating element inside the pump can fail over time, especially in hard water areas like parts of Bournemouth and Poole. Limescale builds up on the element and eventually causes it to burn out. Signs:

• Pump runs normally, filter works, bubbles work — just no heat
• Temperature display stays the same or drops slowly
• No error code displayed

This requires a heater element replacement — a straightforward repair for an engineer but not a DIY job for most people.

Faulty Temperature Sensor (NTC)

If the temperature sensor gives incorrect readings to the control board, the heater may think the water is already at temperature when it isn't. You might see the display show a temperature that doesn't match what the water actually feels like.

Thermostat / High-Limit Switch Tripped

Most hot tubs have a safety thermostat that cuts the heater if the water gets too hot. Sometimes this trips and doesn't reset automatically. On some models there's a small reset button on the pump unit. If you can find it, press it firmly. If the tub starts heating again, the thermostat tripped — which may indicate a sensor problem that could recur.

PCB (Control Board) Fault

The printed circuit board controls everything. If it's partially failed, it might run the pump and display normally but not send power to the heater. This is the most expensive repair (£80-200 for the board itself) but is still cheaper than replacing the whole unit.

Cold Weather: Why Your Tub Takes Forever to Heat

In Bournemouth's climate, outdoor hot tubs heat at roughly 1-2°C per hour — sometimes less if it's cold or windy. That means going from tap-cold (around 10-15°C) to a usable 37-38°C can take 12-24 hours.

This is normal for inflatable hot tubs, not a fault. To speed it up:

• Fill with warm water from the hot tap (max 40°C) — cuts heating time in half
• Keep the lid on at all times while heating — heat loss through an uncovered surface is enormous
• Use a ground mat underneath — insulates from cold ground
• Position out of wind — wind chill strips heat from inflatable walls
• Don't run the bubbles while heating — air jets actually cool the water by introducing cold air

If you've done all this and the temperature still isn't rising at all (not even slowly), then you have a genuine heating fault that needs attention.

Lay-Z-Spa Specific: AirJet vs HydroJet

Lay-Z-Spa models come in two pump configurations, and heating issues differ between them:

AirJet Models (Miami, Cancun, Vegas, etc.)

These have the simpler pump with air bubbles only. The E02 error on AirJet models is almost always a kinked hose or dirty filter. The water flow sensor in these models is sensitive and trips easily.

HydroJet / HydroJet Pro Models (Milan, Hawaii, Maldives, etc.)

These have a more complex pump with massage jets and air bubbles. Heating issues on HydroJet models more often involve the impeller (the small propeller inside the pump that pushes water). If the impeller is cracked or worn, water flow drops and the heater can't work efficiently.

How Much Does a Heating Repair Cost?

Typical repair costs in the Bournemouth area for hot tub heating issues:

• Filter replacement: £10-25 (DIY)
• Flow sensor/switch: £25-50 + labour
• Heater element: £40-80 + labour
• Thermostat/high-limit switch: £20-40 + labour
• PCB/control board: £80-200 + labour
• Typical engineer call-out: £40-80 (often includes first 30 mins of labour)

Most heating repairs fall in the £100-250 range all-in, which is significantly cheaper than a replacement pump (£200-400+) or new hot tub.

When to Replace vs Repair

As a general rule:

• Repair if the tub is under 4 years old and the fault is a single component
• Consider replacing if the tub is 5+ years old, has multiple issues, or the liner is deteriorating
• Always repair if it's a hardshell hot tub (these last 15-20 years with proper maintenance)

A good engineer will give you an honest assessment. We only connect you with professionals who won't push unnecessary repairs.