Is the geyser thermostat the same as the gas valve?

On most gas geysers, yes: the thermostat and gas valve are one unit with the control knob.

Can I adjust the temperature while the geyser is running?

Yes, turn the dial. Changes take effect as the water heats or cools.

Gas Geyser Thermostat and Gas Valve Explained

The gas geyser thermostat (gas control valve) explained

The thermostat on a gas geyser is the gas control valve with the Off, Pilot and On knob. It controls gas to the pilot and main burner, senses water temperature, and contains the safety valve that shuts gas when the pilot goes out. It is the heart of the geyser, and Autopilot works with geysers that use the conventional unitrol-type version.

The knob positions

Off: no gas to pilot or burner.
Pilot: gas to the pilot only, while the knob is held down for lighting.
On (often with temperature marks): the thermostat controls the main burner to keep water at the set temperature.

What happens inside

A sensing probe reaches into the tank. When water cools below the setting, the valve opens gas to the main burner, which the pilot lights. When the water reaches temperature, it closes again. Separately, a magnet valve stays open only while the thermocouple in the pilot flame is hot; that is the flame failure safety.

Common faults

Knob stiff or broken.
Main burner never fires though the pilot is lit.
Water overheats; relief valve discharges.
Gas smell at the valve body: stop using the geyser and call a technician.

Repair or replace

Gas valves are sealed safety components. A faulty one is normally replaced as a unit by a technician, matched to the geyser’s gas type and fittings. Never tamper with or wedge the safety valve.

Thermostats and auto ignition

Autopilot works with all gas geyser models that use the conventional unitrol-type thermostat. The thermostat keeps controlling the water temperature (WARM, HOT or VERY HOT); Autopilot only takes over the pilot’s job of lighting the burner.