Cycling or hunting is the main cause of money wasted. If the gas valve is open for long periods-cold house-and off for long periods-toasty house then you will save money however if the gas valve is constantly on off on off then you are wasting about 20% of the volume of gas on each cycle cause you can't ignite 100% volume of gas so about a fifth of it when gas valve opens goes out the flue unburnt.
If that is happening 50 times an hour then that is an awful lot of unburnt gas simply wasted. Among the worst culprits for cycling are combi boilers with not roomstat and a house full of TRVs. And,an old cast iron boiler with 28MM gravity primaries and no cylinder stat which you can't have anyway ,only way to control the hot water temp is by turning down the boiler stat (more cycling) or fitting a Cytrol valve/Danfos tapstat on the return at the cylinder which is worse than useless.
If that is happening 50 times an hour then that is an awful lot of unburnt gas simply wasted. Among the worst culprits for cycling are combi boilers with not roomstat and a house full of TRVs. And,an old cast iron boiler with 28MM gravity primaries and no cylinder stat which you can't have anyway ,only way to control the hot water temp is by turning down the boiler stat (more cycling) or fitting a Cytrol valve/Danfos tapstat on the return at the cylinder which is worse than useless.