Medium
Lt on Johnson Starley C10d

Your heater is temporarily shutting down because it is getting too hot and needs to cool down for safety.

Reviewed by the BoilerFaultCodes Editorial Team · Last reviewed

Book a service

This fault should be looked at by a Gas Safe engineer within the next week or two. It may get worse if left.

What the manual says

Manufacturer manual

In order to limit the warm air temperature the heater will shut off the burner and Lt will be displayed in the centre of the display.

From this model's manual
Verified against the Johnson Starley C10d installation & service manual.
Plain-English guidance below. Severity, DIY steps, costs and parts are our interpretation to help you act, not text from the manual.

DIY fix possible

Check all warm air grilles/vents are open and not blocked by furniture or curtainsInspect the air filter and clean or replace it if it is dustyTurn the heater off and back on to reset once it has cooled down

Find a Gas Safe engineer
Search the official register →
Boiler cover options

Avoid the next call-out bill

A cover plan would handle faults like Lt: no call-out fees, no surprise bills.

Approved partner
Domestic Appliance Guard
Unlimited call-outs, 24/7 helpline, no price-hike promise
Get a quote →

Affiliate links. We may earn a commission at no extra cost to you.

Related guides you might find useful

Banging / kettling / whistling noise

Each noise points to a different fault.

Read →

Boiler won't turn on — 9-step checklist

Work through these before the call-out.

Read →

Yellow or orange flame — CO safety

Safety-critical — turn off, read this.

Read →