you will have much better back up support if you find a decent installer, discuss with them your requirements and then come to an agreement together as to which boiler is to be installed.
Read what I wrote again. Still stands. Most think Vaillant are the best boilers on the market. The best are Intergas, Atag and Navien. The rest are the equivalent to Ford at very best. The local man will dump you with an Ideal or Baxi, or if you want "quality", a Vaillant.
People on here do not laud Intergas for nothing. They even have weather compensation and Opentherm as standard, and always have done, even 20 odd years ago. No one knew what Opentherm was, never ever connecting it (recently I connect up an Opentherm stat/timer to an Intergas than must have been 15 years old). The Rapid, is the best value on the market in quality bang for buck. I would say to the customer get one of those, then get an installer to quote ignoring his brand advice. Be emphatic in insisting on an Intergas. Guys here may give a local installer.
for completeness for Hard-Work, a Navien NCB 34 is £897.19 from plumbase and comes with a 7 year warranty. They appear to be good and are a very large player in the states, however in the UK they have only been around for a few years and uptake of their boilers has been slow by the trade. Very little information is available about them in the real world from user or installers, so this is very much a left field choice.
If you are near one of Navien's service agents, listed on their web site, they are fine. Parts delivered overnight. Lots of info on the web about Navien in real world use. It does not have to be in the UK. Americans love them. Lots on Youtube as well. Plumbase are a national chain being everywhere. They also sell Intergas as well. The Navien comes with the flue, filling loop and thermostat/controller, the TOC. They use the same flue as Ideal and Intergas.
The NCB 34kW gives 14 litres/min, while the 40kW delivers 16.5. The bigger the better as DHW is guaranteed at two showers.
They are quality. No outside weather sensor or cable in the new units, as they use satellite info for the outside temperature, like your smart phone does. Touch screen displays with even the thermostat talking to you if you want. It can even be fitted outside, the only boiler than can be. One of these in the back garden would make a big difference in small box homes. Few have heard of it. If they had it could have got them out of trouble in finding a decent boiler position, like outside. Their twin pipe extended flue system uses 50mm plastic drain pipe. Only Keston and Navien have such long (110m) and flexible fluing systems.
Beware. Cowboys hide behind brands like Vaillant and Worcester Bosch. The customer only sees the brand.
