7 Factorial – so many options


Seven Factorial (7!) – its a mathematical term which means 7 x 6 x 5 x 4 x 3 x 2 x 1

When looking at a boiler which has developed a fault we are faced with more than 7 different things that could go wrong.

We have:-

1. The pump

2. The circuit board

3. The gas valve

4. The ignition system

5. The Heat exchanger

6. The diverter valves

7. The fan


The “Factorial” function is used to determine the number of possible variation that can exist with the number, in this case 7. The result of 7! is 5040. That is to say that there are 5040 different combination of the 7 parts of a boiler going wrong and stopping it from working.

The heating engineer’s job is to go through a logical sequence of fault finding in order to narrow down the possibilities of each of the above items causing the breakdown.

The diagnostic process varies for each boiler and each boiler manufacturer and so this is a further variable which needs to be computed. To assist the heating engineer there are a host of indicators such as error codes, voltages, resistances and impedances. In addition many manufacturers have excellent technical help lines who can talk you through the faults.


Of course your could ask Google or Siri. But beware, Google only answers a very narrow set of questions you present it. If you don’t tell it that you have very old radiators it won’t take that into account and if you don’t tell Siri that the domestic hot water runs hot then cold then hot again, it too won’t be able to help you. A good heating engineer will ask all of these questions in a subtle and focused way, guiding him/her along the path that eliminated some of the 7 factors that could be making matters difficult for your boiler

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