It's almost Christmas. Time for a Central Heating failure F1.

Almost Christmas. The ideal time for the central heating to go wrong. we were getting an F1 error on the boiler. It means insufficient pressure. 

I did the usual things with a radiator key and that 'U' connector to refill the pipes and it worked again for a bit, but then failed again with the same error.

 I worked out it must be more than a simple DIY problem. Except when I contacted various plumbers no one was available. 

 I had to turn to physics.

The inside of our boiler is like something from NASA. But I realised that there must be an expansion tank inside for the radiator water. Check out the right hand side tank. It can't be simply a reserve tank, because it needs to maintain a certain pressure. 

 That's how I worked out that the expansion tank inside the boiler is cleverer than it looks. And why it has a bicycle tyre valve on it. Check out the middle of the steel tank.  

The water must go into a bladder where it can expand but gets pressurised from surrounding air in the tank. Compress air not water etc. (real physics)  

The expansion tank air, if insufficiently pressurised, won't create the starting pressure for the boiler. 

 So what to do? Don't try this at home etc. I thought it was a case for Joe Blow. I found my bike tyre pump, conneted it to the pressure vessel valve and pumped it to just under 1 bar. It only took about three pump fulls to do this. The boiler pressure was restored and hasn't given any more F1s since. 

An odd repair, strangely satisfying.