The thermostat shows condensation inside the display or housing.

Safety: If moisture is visible inside an electrically powered device, switch off power at the fused spur before removing it from the wall.

Steps:

• Remove the thermostat from its backplate and gently dry the exterior with a soft cloth. Do not use heat guns or hair dryers.
• Allow the thermostat to dry in a warm, dry room for 24 hours before refitting.
• Inspect the wall behind the thermostat for signs of dampness or cold bridging. Improve insulation or relocate the thermostat to a drier internal wall.
• Seal any large cable entry holes behind the thermostat with non‑corrosive sealant or insulation to reduce air movement.

Remedy:

• If condensation recurs and the thermostat behaves erratically, internal corrosion may have occurred; replace the thermostat and address the underlying damp problem.