With a new energy efficient boiler? The london boiler engineer will carry out a gas-tightness test to establish if there are any leaks in the system. This will be useful someday i never knew the pepsi method, will have to try that out if and when my drain gets clogged in the future! The way plumbing should be" is not just our tagline, it drives everything we do. Living the values and being a good example for others. Electric boilers provide a viable alternative.