Error 3P9: the boiler is letting you know its service is due

What it means

Many boilers have a maintenance counter that is set at each service. When the interval is up, the display shows 3P9 as a reminder that the next service is due.

The manufacturer describes it as ‘scheduled maintenance’: it's a reminder to call the service centre, not a warning that something has broken.

Most likely causes

1. The maintenance interval set on the boiler has run out.
2. On its own, it doesn't indicate a fault. If the boiler is also not working properly, check whether another code is showing.

What you can check yourself

Without tools and without opening the unit.

1. Check whether the boiler is working normally. If it's providing heating and hot water, you don't need to do anything else until the service.
2. Check whether any other code appears alongside 3P9: that one could indicate a fault.
3. Find the date of the last service on the certificate or the invoice: it will help when you book the appointment.

It's not urgent, but don't put it off: book the service. The warning is cleared during the maintenance visit, when the engineer resets the counter.