Hamworthy Ignition Transformer 573406125

The Hamworthy 573406125 is an ignition transformer used on Cranborne THI gas boilers. It steps up the low-voltage supply from the control board to the high-voltage spark delivered at the ignition electrode, which lights the burner on a call for heat. It is a control-side component, listed within the boiler's controls group.

• The boiler attempts to fire but there is no spark at the ignition electrode.
• Repeated lockouts on start-up, with the fan and gas valve sequence running but no flame established.
• A weak, intermittent or visibly erratic spark at the electrode.
• Visible arcing, tracking or scorch marks on the transformer body or its terminals.
• Audible buzzing or clicking from the transformer area without ignition.

• Confirm the appliance model is a Hamworthy Cranborne THI.
• Check the part number on the existing transformer matches 573406125.
• Inspect the ignition electrode, leads and connections before assuming the transformer has failed, as a faulty electrode or damaged lead can produce the same symptoms.
• Isolate the boiler from the electrical supply before carrying out any inspection or replacement.