Worcester Bosch Combi Boilers: Any Good?

Are Worcester Bosch combi boilers any good?

They are a safe, mainstream choice, and the reasons to pick one are real. Worcester Bosch's product page for the Greenstar 8000+ Combi publishes a 94% central heating efficiency figure and an ErP rating of A, and the guarantee at the top of the range runs to twelve years when the install conditions are met. Parts and engineers are easy to come by, which matters more than any spec sheet on the day the boiler stops.

Here is the honest other side, because it is what decides whether one is right for you.

• The headline guarantee is conditional. The twelve-year figure you see advertised on the Greenstar 8000+ is the extended guarantee. Worcester Bosch's own guarantee length page puts the standard at eight years, ten with any Greenstar System Filter, and twelve only when the boiler is installed by a Worcester Bosch Accredited Installer or Accredited Partner with that filter. On the Greenstar 4000 the same ladder runs seven, eight and ten.
• The oil model is the outlier. The Heatslave II, in indoor and external forms, is the only oil-fired combi Worcester Bosch makes, and Worcester Bosch's guarantee page gives oil boilers two years as standard, five with a system filter and seven extended. That is a long way short of the gas models, and worth knowing before you commit.
• Worcester Bosch does not publish prices. Its product pages quote no figure at all, so the number that matters is the one on your installer's quote, not the one in any guide.
• A combi is still a combi. It heats water on demand with nothing stored, so the flow is shared between whatever taps are open at the same time. If two showers running together is a normal morning in your house, look hard at the flow rate on the model you are quoted, or ask your installer whether a system boiler and cylinder suits you better. We compare the two in our combi versus system boiler guide.
• Brand does not fix a bad install. The most expensive boiler on a system that was never cleaned, with a flue in the wrong place or radiators that were never balanced, will still perform badly. Ask what the quote includes beyond the box.

The current Worcester Bosch combi range

Worcester Bosch's own boiler directory currently lists eight combi models. The guarantee column below is taken from Worcester Bosch's guarantee length page, which is the page to check before you sign anything, because these lengths change.

One thing worth flagging, because older guides still list it: the Greenstar CDi Highflow does not appear in Worcester Bosch's current boiler directory. If an installer quotes you one, ask whether it is new stock and what the guarantee position is. For a closer look at the mid-range model most households end up with, read our Greenstar 4000 review, or see the rest of the range on our Worcester Bosch boilers hub.

What size combi do I need?

Two numbers matter, and they are not the same thing.

• Output in kW decides whether the boiler can heat the house. It should come from a heat loss calculation for your property, not from a rule of thumb about bedrooms. A bigger number is not a free upgrade.
• Hot water flow rate in litres per minute decides what the shower feels like, and it is capped by the water coming into your house from the mains. A high-output boiler cannot invent mains pressure that is not there.

Worcester Bosch's own ladder is a reasonable starting point: the Greenstar 2000 and 4000 are pitched at small to medium homes with one bathroom, the CDi Compact at busy two-bathroom homes, and the 8000+ at the largest family homes, with outputs up to 50kW. Use that to sanity-check a quote, then let the installer's survey set the final figure.

There is also a legal floor to be aware of. Under the Boiler Plus standards that apply in England, government guidance states that "the new minimum performance standard for domestic gas boilers in English homes will be set at 92% ErP", that timers and room thermostats are an explicit requirement, and that when a gas combination boiler is installed one additional energy efficiency measure is required, chosen from flue gas heat recovery, weather compensation, load compensation, or smart controls featuring automation and optimisation functions. See the government's Boiler Plus factsheet. If a quote does not mention controls at all, ask why.

What does a Worcester Bosch combi cost?

Worcester Bosch does not publish a price on its product pages, and any fixed figure in a guide dates quickly, so we are not going to invent one. What we can tell you is what the number on your quote is actually made of, so you can compare two quotes properly:

• The boiler itself, and the flue kit for your wall or roof.
• Labour, which varies by region and by how awkward the job is.
• A Greenstar System Filter, if you want the longer guarantee. It is an extra line on the quote and it is the difference between seven and eight years on a Greenstar 4000.
• System work: flushing or cleaning the existing pipework, replacing radiators or valves, upgrading the gas supply pipe, or moving the boiler to a different wall. Moving it is usually the single biggest jump in price.
• Controls, which Boiler Plus makes compulsory on a new combi in England.

Get two or three quotes, insist they are itemised, and check each installer on the Gas Safe Register before anyone touches the gas. Only a Gas Safe registered engineer may legally work on a gas boiler in the UK. If you are weighing a new boiler against fixing the one you have, our guides on repairing versus replacing a boiler and on what a boiler service costs are the two to read next. If it is the boiler you already have that you want covered or repaired, tell us what you need and we will come back to you.

How long is the guarantee?

Between seven and twelve years on the current gas combis, and two to seven on the oil ones, depending on how the boiler is installed. Worcester Bosch's guarantee length page sets it out as a ladder:

• Standard. Eight years on the Greenstar 8000+ range; seven on the Greenstar 4000, the CDi Compact and the 8000 F; seven on the Greenstar 2000 when it is fitted with a Worcester Bosch or third-party system filter; two on the oil boilers.
• With any Greenstar System Filter. Ten on the 8000+ range, eight on the 4000, CDi Compact and 8000 F, five on the oil boilers.
• Extended. Twelve on the 8000+ range and ten on the 4000, CDi Compact and 8000 F, but only when the boiler is installed by a Worcester Bosch Accredited Installer or Accredited Partner with a Greenstar System Filter. Worcester Bosch also states that an installer in its loyalty programme who is not accredited can obtain the extended length by paying an additional £40 through their loyalty account.

So the practical advice is simple: before you accept a quote, ask the installer in writing whether they are Worcester Bosch accredited, whether a Greenstar System Filter is included, and what guarantee length that combination gives you. The difference is years, and it costs nothing to ask.

Two more things people get caught by. A manufacturer guarantee covers the boiler, not your whole heating system, and it comes with conditions, so it is worth reading what a boiler warranty does not cover and knowing how to check what you have left. Our Worcester Bosch guarantee page covers registration.

What goes wrong with them

Worcester Bosch combis report faults as a code on the display, and the code is the first thing an engineer will ask you for. Write it down before you reset anything. We have written up the common Greenstar codes on our Worcester Bosch fault codes page, and the complaints that bring most people to this site are the ordinary ones: pressure dropping over the winter, no hot water while the heating still works, a boiler that fires and then locks out, or a room thermostat that is not talking to the boiler.

What you can safely do yourself is short, and that is deliberate:

• Check the pressure gauge and top the system up only by the method in your boiler's user guide.
• Check the room thermostat has power, is calling for heat, and is set above room temperature. Our guide on setting a Worcester thermostat walks through it.
• Reset the boiler once, exactly as the user guide describes. If it locks out again, stop. A lockout is a safety response to something the boiler has measured, and repeated resets only hide the pattern the engineer needs.
• Anything beyond that, book a Gas Safe registered engineer. Never open the case or touch the gas side yourself.

If you smell gas, do not reset the boiler and do not switch anything electrical on or off. Call the National Gas Emergency Service on 0800 111 999 straight away.

If it is already broken, our no hot water and boiler repair pages cover what happens next.