Our builder installed a new boiler (Vaillant Ecotec 630) 10 months ago. Previously we had the pressure drop after bleeding rads. For the last couple of weeks we've had the pressure drop every 3-4 days. We looked for a leak but nothing obvious. Then we happened to be outside when the boiler started and this surge of liquid shot out of the flue. I contacted both the heating company that installed it and the builder. The heating company never return my calls and the builder said he would chase them. A week later he has asked for a video of the problem! The thing is we don't know when/how often this water spurt is happening. Could the spurts of fluid out the flu be causing the low pressure? Is this something that needs urgent attention? We are loathe to spend out for someone new to investigate but also feel this builder doesn't care or want to check.