Gas Pressure Question...

The boiler should have its own supply directly back top the meter.

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Sounds like one of two likely possibilities: Either the dynamic gas pressure (i.e. under load) is falling below spec at the supply from your meter, or the cooker and boiler at some point share a common pipe, and that pipe is undersized.

If you have a manometer you could look to see what happens to the gas pressure at the meter test point when the boiler kicks in (it ought to sustain 21mbar or thereabouts). If it does not then you need to talk to Transco since it is their problem.

If the pressure at the supply end looks ok, then you may need to investigate what is going on with the piping. Full details of how to calculate the sizing can be found here:

This is not explicitly necessary provided that the pipe system is designed correctly. The applicable British Standard does not require it, and one can look up a design guide based on it at the Copper Development Association.

In this instance, the pipework may be of inadequate size, and *a* solution may be to make a run of pipe from boiler to meter directly. Another is to replace the piece from the tee for the hob and the meter.

... but as a rule of thumb for a boiler up to about 28kW (100,000BTU) the pipework should be 22mm for most of the way to the boiler, up to about 15-20 metres max of pipe run. 15mm pipework causes a _lot_ extra pressure drop.

To get a noticeable effect like you have you will have a significant fault with the supply or pipework.

If you are competent to do so (see FAQ) you need to see what is going on with the gas pressures at the meter and the appliance inlets (boiler will have a test point whilst the cooker may not). HTH