Vaillant boiler fault F28 or F29

[steveburrows]

Just in case anyone has a similar problem, I had a problem with my new Vaillant Ecotech boiler (condensing one)
Its caused by the condensing pipe freezing and blocking with ice (mine runs outside the house, its 22mm and covered in pipe insulation)
The recent freezing weather (it was -11 this morning) has caused it to freeze up twice in the last 2 days. Yesterday i thawed it with boiling water from the kettle, and got it running again. Today it froze again, so i hacksawed the pipe a couple of inches from where it exits the house.
If the condensing pipe is frozen, the condense trap fill up and the boiler will not work, and shows a F28 or F29 fault code.
Hopefully it wont happen again.
Hopefully this will save someone a massive plumbers bill.