Replacing boiler

Since April Fools day this year...yes. I don't think it's the mother of all April Fool's jokes either.

Unless you've got a very special reason to be exempted.

Generally yes, but there are exceptions. Check out the assessment procedure document, link from

By the book yes.

However: There still seem to be plenty of people around who will supply and fit a non-condensing unit. Very little paperwork of course and the warranty (probably) won't exist if you need it. The plumbing shop at the end of the road here is selling (Heatline IIRC) Combis for 310+VAT . They have this in Bright Orange letter on the wall outside.

As I suspected, locally at least, the market is splitting into distinct upper and lower segments.

Nope. The book does not state fully pumped. There is one condensing boiler that can give gravity DHW, although I would advise against it.

The heating coil for the cylinder may well have to be pumped, but this makes sense anyway, as you can then accurately control the temperature. The hot water itself can still be gravity fed as this makes no difference to the efficiency.

That's what I meant.

By pumped, it means that the circuit to the hot water cylinder coil must be pumped. You can continue to have the hot water itself fed by gravity to the taps if you wish.

The idea is that this heats the cylinder up quicker, so the boiler spends more time off and the circuit pipes stay colder for longer, so don't waste heat.

Christian.

Then I'd certainly go for that, as it has been good practice for perhaps

Which is about how long it is since I installed the system!

How is the pumped DHW circuit incorporated? Is there one pump on one flow from the boiler with the pump outlet diverted to CH/DHW/both by a motorised valve?

Yes - perhaps the most common is a three port valve. Although you could use two motorised types. Or even two pumps. ;-)