Choosing a new combi boiler soon, either Worcester Bosch or Vaillant, is one better than the other?

[soberton]

Hi
We will need to install a new combi boiler soon ahead of having our loft conversion done (all plans and structural calcs are completed and approved by local council) just waiting to book a start date.
A Gas Safe Heating Engineer called last week to quote us for removing the old immersion tank in the 1st floor airing cupboard, the two water tanks in the loft and the very old (probably 30yrs ish) boiler down in the kitchen. He said that it's quite a straight forward job which he has done many times before, he will need to update gas supply pipes as the old ones are narrower.
He has been recommended by the loft conversion company as he comes in to do a lot of plumbing/gas work for them and said that he will more than likely be putting in the new en-suite on the 2nd floor for us (so it makes sense for him to deal with the whole plumbing/heating side of the job & follow the chain through). The old airing cupboard on the landing has to go in order to make room for the turner steps of the new staircase which will go up over the original one.
He has recommended a Worcester Bosch combi boiler as he has one in his own similar spec house and is happy with it. When I mentioned what about Vaillant? he said that they were both good brands although Vaillant often comes up a bit more expensive, but he will check and provide me with a written quote for both. The new boiler needs to supply heating & water for 3 floors eg ground floor = 3 rads, boiler & kitchen sink, 1st floor = 4 rads & bathroom (WC/handbasin/bath) and the new 2nd floor = 2 rads & en-suite (WC/handbasin - the shower there will be electric).
Would like opinions over the two brands, is one better than the other or is it personal preference?
TIA

I have the Bosch for about 6 years now no problems. I think most plumbers recommend as they are very reliable.

Soberton I need to do exactly the same thing soon (new boiler, remove tanks) - may I ask how much you were quoted please?

heating engineers are very argumentative souls and can never agree which is best.

They do however agree that quality of installation is the most important thing. You are putting a new boiler on an old system, so it will be full of sludge, sediment, corrosion and rust. So before fitting the new boiler the system needs to be powerflushed, and I strongly recommend that you have a system filter fitted on the return to the boiler to catch the remaining particles before they can accumulate into a blockage or cause wear. Modern boilers are much less tolerant of dirt than old iron boilers were, and some are very difficult to clean out. Boiler problems caused by dirt will not be covered by the manufacturer's guarantee.

Piglet said exactly what I thought when I read the title.
A good install is more important than the brand of boiler - system clean, chemical inhibitor in the system.

If you have any cash to spare it will be worth replacing any of your really, really old rads too, they are not efficient.

We went for Worcester Bosch to replace our 19 yo Worcester Bosch. The plumber recommended all the things PigletJohn and MrsT has said and we were very happy with paying a bit extra for the power flush and filter.

Thanks for all your replies - I was hoping that PigletJohn would be around. The engineer was here for about an hour on Friday afternoon. He looked at all the radiators around the house and stipulated that they would all need to be power flushed, including the pipes between them. he said that not to do so would invalidate the warranty on the new boiler and that he also fits a filter (and mentioned the word magna - not sure if that's part of the flushing process or the filter). He will prepare fixed quotes for both makes which I should have by the end of the week, so I will keep you posted. I was reassured by the fact he said that the price he quotes is the price he will honour - even if he does find something awry under the floor boards etc or as he said "that's my problem, not yours". Two of the existing radiators are only a few years old and the others are always quite responsive when the heating comes on. He did also mention that it's good all the bedroom ones have adjustable valves on them because that meets new building regs (only for bedrooms apparently, the others around the house don't have to have them, although it is obviously usefull if they do).
Thanks for all your replies and I will post again when I get his quote.

he might have said Magnaclean. It was the first mass-market filter, and is spectacularly fast at collecting black sludge. Ask him to show you how to open it and remove the dirt it has collected (it needs doing at least once a year, and is about as easy as emptying a hoover).

The early versions were notorious for leaks, but I am assured that the current version is improved. There are a few other makes, but they all have magnets in now.