How does a thermocouple have enough power to operate a gas valve?

Common sense tells us it can't be. A quarter of a 1 bar fire would make the water in the boiler pretty warm! Now remember that at this point the pump isn't running, so that heat can't easily move to the radiators. The boiler would get piping hot pretty quickly. My medium sized gas boiler is rated 4-12kW (depending on the gas pressure setting), which would mean it's still using up to a 16th of the gas when turned off! That would be truly absurd. The only thing as stupidly inefficient as that is a Sky satellite TV box which uses precisely the same 38W when in standby as when switched on!

Oh I don't know. In the dim and distant past, my boiler which had a pilot light was floor standing and about 0.6 x 0.6 x 1 metre high. Giving it a surface area of about 2.4 square metres. Much bigger than a modern boiler I know, but modern boilers don't have them. So, taking a convective heat transfer coefficient of 10 W/m^2K the surface temperature rise to dissipate 250 watts if it does not go anywhere else is about ten degrees C. Warm to the touch but not huge. And I bet 90% of the energy used to go out of the flue.

In the mid 70's I had a multipoint gas water heater which, IIRC, was 22 kW. The exposed surface was probably only half that of the boiler in the calculation, but that had a fairly lively pilot light and the casing was always perceptibly warm to the touch.

I once calculated my gas usage for the pilot light to be £10 a month (at 3.5p a kWh) on my 12kW boiler, as it was the only thing running over the summer. That's a ridiculous cost, no wonder they use electric ignition now. Not sure why they didn't always do that - gas cookers have had spark ignition for at least 40 years, if not more. Even if they didn't have a spark that could operate millions of times, it could always light a pilot and extinguish it if not in use for a certain amount of time.

Not to worry, ain't no more of them.

Back 1975ish there were some installed (afraid I have no idea of the number [a]) in patients because of the issues of standard battery life.

This was a short term program due to a bunch of coinciding issues:

a: huge cost involved b: standard batteries got _much_ better around then, both in regards to power density and life span. Oh, and leakage. c: the Nuclear Regulatory Commission required radiation licensing/certification of a big number of the people involved in the process. In other words, it wasn't like a standard pacemaker which any (competent) medical/surgical/cardiac physician and facmility could install and monitor.

It's just barely, barely, possible there are a handul still in operation. Make that a thimbleful.

It's quite likely that some were buried with their recipient's bodies...

Oh, there was an episode of Emergency [b] where Roy and Johnny had a patient using one.

I don't recall offhand what problems they were concerned with.

He didn't say to power the spacecraft he said 'for power'.

Bill

So it moves by magic then?

Very few spacecraft are electrically powered.

Whatever they're powered by should be able to give off some electricity, like a petrol car does. You don't have to fill the battery do you?

Its no good arguing with the Kernel, he is a troll and a comedian, but not really interested in any discussion about facts. Brian

So they don't have any manoeuvring thrusters?

They could do, and very effectively.

Could also just have solar panels.

Your choice of words continues to amuse me.

If something happened on earth that required intelligence to survive, the stupid would die off.

A few of those could power a house.