Brand new boiler was faulty for the first 2 months. Warranty engineer was out 3 separate times before he found the part in the boiler that was faulty. He blamed it originally on the water pipes and valves in the house. Thankfully he was made to be convinced everything in he house was fine and he took the boiler to bits to find that a disc was loose in the boiler allowing water to pass both sides. Our installer spent hours and days triple checking things he said were right in the first place until he eventually manage to convince the Viessmann warranty engineer.