Vaillant ecoMAX 646 Service Manual download pdf (Page 47)

Sheet C Check Central Heating control and external controls

Does yellow central heating demand indicator ( ) glow?

Does burner light?

Go to Sheet D

If the yellow central heating demand indicator ( )

still does not glow, replace main switchboard

Go to Sheet H

Check central heating control switch is set to position ( )

Is 230 V AC present across boiler

terminals 4 and 5?

External fault. Check whether all external controls are

calling for heat, replace or repair as necessary

(see also note 1, sheet A)

Yes

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Vaillant ecoMAX 646 Service Manual Page 47