Daikin outdoor unit not heating

[goose1]

Strange one this, I've linked out A & C on two Daikin outdoor units using a non volt relay to change from cooling to heating dip switch 1 set to outdoor . On one system it works fine the other one just displays fan mode .
Any ideas if it's a field setting I need to change?
Works fine on cooling .

[frank]

Sounds like you have B & C connected. See page 14 https://www.google.com/url?sa=t&source=web&rct=j&url=https://www.daikin.co.uk/content/dam/document-library/installation-manuals/ERQ-AV1_4PWEN51321-1B_2018_04_Installation%2520manual_English.pdf&ved=2ahUKEwjJ4bnTs6PtAhXWRBUIHQAnBwgQFjABegQIAxAI&usg=AOvVaw2ACYQArqFOwmd7jqGZPwD7&cshid=1606503568684