Vaillant turboMAX pro 24/2 E Instructions For Installation And Servicing page 32

Ensure that radiator temperature control knob
is set to vertical position and that any internal
timer (if fitted) is calling for heat
Does yellow central heating demand
indicator glow?
No
Is 230 VAC present across terminals 4 and 5
No
External fault: Check all external controls are
calling for heat, replace or repair as necessary
(see also note 1 sheet A)
Check central heating and controls
Does yellow flame indicator flash?
Yes
Yes Disconnect built in timer (if fitted)
Sheet C
No Go to sheet D
No
Does ignition
commence?
Yes
Replace defective
timer