Worcester Bosch vs Vaillant: which should you have fitted?

Two quotes land. One has a Worcester Bosch on it, the other a Vaillant. It is the most visible difference between the two pieces of paper, so it feels like the decision.

In practice it is usually the smallest difference of the lot. Both sit at the top of the UK market, both are boilers a good installer is happy to put their name to, and neither is a mistake. The things that decide whether you are still pleased in five years are mostly somewhere else on the quote.

That does not mean the choice is meaningless. It means the useful questions are narrower than "which brand is better", and most of the answers are not on the brochure.

The guarantee on the brochure is not the guarantee you get

This is the single most important thing to understand before you compare two branded quotes, and it is the reason two installers can quote the identical model and leave you with different cover.

Worcester Bosch publishes different guarantee lengths for different products, and the longest lengths are conditional. Reaching them depends on the accreditation your installer holds and on a Greenstar system filter going in with the boiler. An installer outside that accreditation is not quoting the same guarantee, even with the same appliance in the box.

Vaillant works differently. The length is tied to the boiler being registered within 30 days of installation, and Vaillant's own terms are blunt about what happens if that window is missed: the guarantee reverts to 12 months from the installation date. Their terms also require the Benchmark logbook to be completed at the point of installation and kept on site, and an annual service to be arranged to keep the cover valid.

So the fair question to put to both installers is not "what guarantee does it come with". It is "what guarantee will I actually hold, what has to happen for that, and will you write it on the quote". An installer who answers that clearly is telling you something useful about how they work.

Source: Worcester Bosch, guarantee length; Worcester Bosch, guarantee terms and conditions; Vaillant, domestic boiler guarantee terms and conditions; Vaillant, guarantee registration

Both of them expect you to service it

Neither manufacturer offers cover that survives being ignored. Both make continued guarantee cover conditional on the boiler being serviced in line with their instructions, which in practice means once a year, by someone qualified, with the record kept.

It is worth knowing this before you choose rather than in year four when a part fails. A long guarantee is not a promise that nothing will go wrong for that long. It is a promise that the manufacturer will deal with it, provided you have kept your side of an agreement most people never read.

The filter is not an optional extra on either one

On the Worcester side, the system filter is part of how the longest guarantee is reached, so a quote without one may quietly be a quote for a shorter guarantee than the one you were shown.

On any brand, the industry code of practice for domestic heating water, BS 7593, sets the same expectation independently of the badge: clean the system, add an approved inhibitor, fit an in-line filter, and keep the inhibitor topped up afterwards rather than dosing it once and forgetting it.

If one quote lists cleaning, inhibitor and a filter as named lines and the other does not, you are not comparing two brands. You are comparing two different jobs, and that gap will show up in the price long before the badge does.

Source: HHIC, maintaining a healthy and efficient domestic heating and hot water system

What actually decides whether you are happy in five years

Every installer we place work with would put these ahead of the brand, and none of them are on the front of a brochure.

• Whether the boiler is sized to the house rather than copied from the old one.
• On a combi, whether your mains flow rate can actually feed the model quoted. A powerful combi on a weak supply is a disappointing shower whichever badge is on it.
• Whether the system was cleaned properly and protected, so the new boiler is not inheriting the last one's problems.
• Whether the flue route and termination were looked at rather than assumed.
• Who is fitting it, and whether they will still answer the phone in March.

So which one should you pick?

Pick the installer first, then the boiler. If both quotes come from people you would trust in your house, choose on the guarantee you can genuinely hold, on whether the unit physically fits where it needs to go, and on whether the model suits your water supply and your heat loss. On those grounds the answer is different in different houses, which is exactly why nobody can honestly tell you one brand wins everywhere.

What we would not do is treat the badge as the reason one quote is dearer than the other. The appliance is the most comparable line on a boiler quote and the least likely explanation for a gap between two prices.

Getting a like-for-like comparison

The cleanest way to settle it is to have both options quoted properly by installers who have seen the job, with the guarantee length and its conditions written down in each case. Then the comparison is real rather than a brand argument.

Tell us about your home and we will arrange up to three quotes from vetted local installers. Ask each of them what guarantee you will hold and what has to happen for it, and you will learn more from the answers than from any brand league table.