TTB Downdraught Thermostat Emergency

Ideal TTB Downdraught Thermostat Fault Code

Also written as TTBDOWNDRAUGHTTHERMOSTAT — same fault.

The Ideal TTB Downdraught Thermostat fault code means: your boiler has shut down because wind or a blockage is pushing harmful exhaust fumes back down the chimney instead of letting them escape outside.. It appears on 1 Ideal model in our database.

Act immediately

Turn off your boiler and stop using gas appliances. Call a Gas Safe engineer now. This fault can be dangerous if ignored.

Technical description: If this thermostat should operate and switch off the appliance it is because the flue is subject to downdraught, probably as a result of adverse wind conditions. It is an automatic reset thermostat with a built-in reset delay in excess of 10 minutes.

What causes the Ideal TTB Downdraught Thermostat fault?

This fault occurs when the safety sensor detects that poisonous combustion gases are failing to rise up the chimney and are instead spilling back into your home. The most common reasons are a physical blockage in the flue, such as a bird's nest, or severe wind conditions pushing the air back down the pipe.

This issue is most frequent during autumn and winter when high winds are more common or when debris like fallen leaves and nests block the chimney.

Typical repair cost £120-250 (including labour)

Engineer required

This fault requires a Gas Safe registered engineer. Do not attempt gas-related repairs yourself.

Find a Gas Safe engineer

Search the official register for a qualified engineer in your area.

Gas Safe Register →

Ideal models that show the TTB Downdraught Thermostat fault code

Click a model for the full fault code list and model-specific repair notes.

Source

Ideal TTB Downdraught Thermostat fault code information on this page is sourced and cross-checked against the official Ideal service / installation manuals for each affected model.

Reviewed by the BoilerFaultCodes Editorial Team · Last reviewed 27 April 2026