Financial payback times of half a year or less can be realized at low investment costs. One can expect to need a working time of two hours to two days to do the tests and to install the switches as described in this instructable.
Note that safety restrictions apply and that a few additional conditions must be met (see step 2 in this instructable).
After measuring your own combi boiler stand-by and cold start consumption, and comparing this with your average daily domestic hot water demand pattern, you’ll be able to calculate the benefits of applying the concept from this instructable to your combi boiler. Generally speaking, the smaller your house is, the larger the relative benefits will be. If you don’t use hot water a lot, benefits of omitting stand-by losses will be higher. The higher the natural gas prices you pay (including energy taxes), the more benefit you’ll experience from the energy savings. You may expect net annual savings of $ 7 to 24 per year in the United States, EUR 10 to 36 in the average European Union and EUR 12 to 43 in the Netherlands.
The concept of the circuit described here is made available through a Creative Commons Attribution license (CC BY); the innovative part of the design is explained in step 1 below. For commercial use some directions have been provided in the last section of this instructable (step 8).