UK trade guideShower Spares 4 min readUpdated 11 July 2026

How to Replace the Thermostatic Cartridge on a Bristan Bliss 3 electric (UK)

UK guide to swapping the thermostatic cartridge in a Bristan Bliss 3 electric shower valve. TMV2 compliance, part numbers, tools.

Bristan

The part

Rebalance a scaling Bristan Bliss 3 electric by swapping the OEM thermostatic cartridge — restores TMV2 approval and 38 °C set-point.

Isolate

Isolate hot and cold at the built-in EasyFit valves or dedicated isolators. Drop the pressure by opening the outlet fully.

Swap the thermostatic cartridge

Undo the temperature handle grub screw, remove the escutcheon and pull the cartridge with the OEM extraction tool — needle-nose pliers will crack the Bristan plastic housing.

Commission

Balance hot and cold to within 0.5 bar. Run the Bristan Bliss 3 electric at max flow for 3 minutes.

Verify max outlet temperature stays below 46 °C per BS EN 1111 by shutting off cold and reading the outlet.

Frequently asked questions

How do I set the max temp?
After fitting, run cold-only, then set the shroud to 38 °C, then hot. Rotate the stop-ring until 43 °C max is achieved at the outlet.
TMV3 compliance?
The Bristan Bliss 3 electric cartridge is TMV2 approved out of the box. For TMV3 (healthcare) fit the -HC suffix variant.
OEM or aftermarket for Bristan?
For TMV2/TMV3 compliance always fit genuine Bristan cartridges. Aftermarket voids the Bliss 3 electric approval.
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