Megaflow problem - is it thermostat?

FreeBear

https://forums.moneysavingexpert.com/discussion/comment/81975617#Comment_81975617

My eyesight is going. Indeed, S40/4 - Now obsolete and replaced by the Wilo Yonos MAXO 40/0.5-4. Best price I could fine is around £700.

If a new capacitor is all that is needed, that will be a lot cheaper than a replacement. Should the motor be burnt out, it may be possible to get it rewound. Likely cheaper than a new pump as long as the pump body is still in good order.

WIAWSNB

More likely it'll be the bearings that'll fail first, but I would imagine there are refurbishing companies for this too.

Of course, we all know the pump is gonna outlast everything else…

ComicGeek

The 40 code normally refers to the flange diameter (in mm), so would expect to see a 1.5" (internal) pipe connection if it's old imperial sizes, which would be nearly 2" outside diameter.

The 4 code normally refers to the maximum delivery head of the pump, which would be 4m here - this is how high the pump can push the water. 4m is very low, unless it's only a 2 storey house with all upper floor radiators fed from below. Might be worth checking before you spend any money on it.

TheGreenFrog

https://forums.moneysavingexpert.com/discussion/comment/81976052#Comment_81976052

The pump is below ground and the highest radiator is probably about 9-10 meters above the pump!

It could well be an underspecified pump but it has sort of worked over many years so I have not had cause to question it. But it also appears that the pump is for a smaller diameter pipe than the size that actually comes out of the boiler. The pipe from the boiler has an external diameter of 60mm, but between the gate valves of either side of the pump the pipe seems a bit smaller (hard to see with all the lagging). So if for some reason it does need replacing then maybe I should get someone who knows what they are doing to work out what pump is needed!