My boiler is now two and half years old. It went into shut down 3 weeks ago. I called vaillant and of course had to take out instant cover insurance to get them in the door STG299. when the engineer arrived he noted the seals had melted along with a large black plastic tube like thing. He replaced the seals. Managed to get money refunded as a design fault. One week later. Pressure is going up on the boiler. Call them back with that problem. seals had melted again. This time he also replaced the heat exchanger. the pressure had gone up again. I've tried to call them but they obviously have a problem with their phones. Do I have a duff boiler and should insist on a complete replacement? It will be interesting to see if it has melted again, but that doesn't explain why the pressure is going up? or does it? Please help. Thanks