I am not a gas engineer.

This information is for discussion purposes only.

Use it for debate with your Corgi friend. Do not try it yourself unless you are SURE what you are doing, and at your own risk.

Usually a pumped system (as distinct from a gravity or semi-gravity system) will not run without the pump for one of two reasons. First the absence of circulation results in localised overheating and an internal overtemperature sensor turns it off. If that overtemperature switch did not work you MAY have burned holes in the firebox walls and the boiler is dangerous to use and dead unless you know a really good welder who is not going to charge you, and it's a sod of a job to remove the firebox for welding and put it all back again. Assuming that is NOT the problem and the overtemperature switch is just feeling grumpy, you can SOMETIMES re-light by using a reset button. Second, some cleverer systems have a circulation sensor. No circulation, no light of main firebed.

Gas boilers need electrical mains to run their electronic controls. Have you checked that there is electricity where there ought to be?

However, it looks as if your pilot light is off. Pilot light re-lighting usually requires the holding down of a control valve or button while pushing a piezo igniter. Piezo igniters can be little devils. If there is safe access for a taper to where the pilot ought to be, it MAY be worth holding down that control valve and putting a taper to the pilot and seeing if the pilot light lights. Hold the valve down for DOUBLE the period the instructions say. This is because near the flame of the pilot light should be a little temperature probe that shuts off the gas to the main firebed unless the pilot is alight, and it needs to get hot. Then slowly release the valve. In case of failure repeat with larger flame on taper. This is what I have to do usually to get my caravan gas fire alight!

My old swimming pool boiler (I sold that house since and downsized) would let you use a more dangerous trick. If you put a BIG flame on where the pilot light ought to be, you could while holding that flame there, gradually turn the control valve and light the main bed with a big thud. Once the main bed was alight it would often create enough background heat to keep the gas on even though the pilot was dodgy. Once the thermostat (or any other of the controls or safeties) turned the main bed off however, it all cooled down again so it was repeat trick to re-light.

If the pump is dead (you should be able to test that by connecting the pump to a source of mains electricity and feeling for a faint vibration: no vibration, pump is not going round. Simplest way to check mains is to take the connection cover off and check for mains on the pump motor with a voltmeter) it may just be stuck. You should be able to get at a slot in the end of the motor shaft (usually up the same end as the bleed screw sometimes the opposite) with a screwdriver to turn the shaft. You may need to do it with the power ON. That maybe enough to get the pump motor running. If not there should be shutoff valves and screw threaded insert points that make the changing of the pump only half an hour's work. Put a kitchen pan underneath to catch the cupful or so of water that will come out when you loosen the threaded instert points. A pump is about £15 to £20 at a plumber's or builder's merchant. It maybe worth paying a bit more for a Grundfoss Gold.

But didn't your Corgi friend know/do all this anyway?