Worcester Bosch Greenstar 25i: Honest Review

Is the Worcester Bosch Greenstar 25i any good?

It is a well built, easy to live with combi that was aimed squarely at small homes, and the published numbers back that up. Worcester Bosch rate it at 24kW of heating output and 9 litres of hot water a minute, with a seasonal space heating efficiency of 94% and an A energy efficiency class. For a one bathroom flat or a small house it does the job, with a declared sound power level of 50 dB(A) indoors.

The honest weaknesses matter just as much. Nine litres a minute is at the low end for a combi, so a second tap will noticeably weaken the shower. Hot water is limited to a 40 to 60°C range, and the boiler needs 1.3 bar of working mains pressure to reach its full flow, so a weak incoming main makes the same boiler feel worse. Above all, the Greenstar i range is no longer sold: it does not appear in Worcester Bosch’s current combi line up or on their published guarantee lengths. Every 25i out there is now an ageing boiler on borrowed time.

Two design details are worth knowing about. Its components are front accessible for service, so an engineer does not have to take it off the wall to reach the expansion vessel or the pump, which keeps labour time down. And it has a large capacity siphonic condensate trap, which reduces, though it does not remove, the winter freezing problem that puts so many combis out of action in a cold snap.

What size home does a Greenstar 25i suit?

One bathroom, and one hot tap at a time. A combi heats mains water as it flows, so the figure that decides whether you are happy is the hot water flow rate, not the kW badge on the front.

Worcester Bosch fit the 25kW model with a flow regulator set to deliver 9 litres a minute at a 40°C temperature rise, which is a realistic winter figure rather than a flattering summer one. Its bigger sibling, the 30i, is regulated to 11 litres a minute. The boiler also needs a minimum flow of 2.9 litres a minute at the tap before it will fire for hot water at all.

Note that both models put out the same 24kW for the radiators. The difference between them is hot water, not heating. If your home has two showers, or you regularly run a bath and a kitchen tap together, read our Worcester Bosch Greenstar 30i review instead, or look at a system boiler with a cylinder.

Whatever a size chart suggests, the correct boiler for your house comes from a heat loss calculation and a measured flow rate at your kitchen tap. That is your installer’s job, and by law the installation itself must be carried out by a Gas Safe registered engineer.

How efficient is the Greenstar 25i, and what does it cost to run?

Worcester Bosch’s own ErP datasheet puts seasonal space heating energy efficiency at 94%, in energy efficiency class A, with hot water also rated class A on the XL load profile. A is the top band on that label, so a like for like swap to a brand new combi will not transform your gas bill.

Where you can still find savings is in how it is run. The same datasheet shows useful efficiency of 99.4% at 30% of rated output in the low temperature regime, against 87.7% at rated output in the high temperature regime. In plain English, the boiler is at its most efficient ticking over at a lower flow temperature and least efficient running flat out. Turning the central heating flow temperature down and letting it run for longer costs nothing, and it is the single change that gets the most out of this boiler.

Other published figures worth knowing: standby heat loss of 0.058 kW, NOx emissions of 44 mg/kWh, and a SEDBUK 2009 rating of 89.6%.

What does a Greenstar 25i cost now?

There is no current Worcester Bosch price, because they no longer sell it. The Greenstar i range is absent from their present combi line up and from their published guarantee lengths, so anything advertised as new is old stock. We do not publish boiler prices on this page, because a real figure depends on your flue route, gas pipe size and the state of your existing pipework, and any number that ignores those is guesswork.

For most people reading this, the live question is not the purchase price but repair against replacement. What actually moves that decision is the age of the boiler, whether the specific part is still a stocked item, and whether any guarantee still runs. Worcester Bosch also exclude “any repairs not authorised in advance and in writing by us”, so check the guarantee position before you agree to any work. Our guide on whether to repair or replace a boiler works through that arithmetic.

How long is the Greenstar 25i guarantee, and is mine still valid?

It depends on when yours was installed, and here is how to check rather than guess. Worcester Bosch’s current guarantee lengths page lists the Greenstar 1000, 2000, 4000, CDi Compact, Ri, 8000 F and 8000+ ranges. The Greenstar i is not on it, which is what you would expect of a range that has been withdrawn.

Three conditions in Worcester Bosch’s own guarantee terms and conditions catch people out:

• Registration. “The Product must be registered with us within 30 days of installation.”
• Annual servicing. “The Product must be serviced annually by Bosch or any other competent and officially certified engineer”, with the details recorded in the service record.
• Repairs and alterations. “Any repairs not authorised in advance and in writing by us” are excluded, and the boiler “must not be moved or relocated, including within the same property, without our written authorisation”. Either can reduce, limit or invalidate the guarantee.

To check yours, find the serial number on the appliance identification label on the boiler facia, then contact Worcester Bosch guarantee registration on 0330 123 2552, or their technical helpline on 0330 123 3366. Our Worcester Bosch warranty check guide sets out what to have to hand before you call.

What goes wrong with a Greenstar 25i?

The Greenstar i displays an alphanumeric fault code alongside a three digit cause code, and Worcester Bosch ask you to quote both, for example “EA and 227”. These are the ones that come up most often on an ageing 25i, taken from Worcester Bosch’s own error code tables.

The middle column is Worcester Bosch’s own wording. The right hand column is what these codes usually turn out to be on a call out, which is engineer experience rather than anything Worcester Bosch publish.

What you can safely do yourself

Three things, and no more. Check the pressure gauge on the facia, and if the needle sits below 1 bar, top the system up at the filling link until it reads between 1 and 1.5 bar. If it is safe to reach, check the condensate pipe outside for ice or a blockage. Then press the reset button briefly, once. Worcester Bosch distinguish a locking error, which needs one manual press of the reset button, from a blocking error, which clears itself once the fault clears. A lockout that comes straight back needs an engineer.

Do not touch the gas valve, the burner, the flue or any sealed component. That is work only a Gas Safe registered engineer may legally carry out. If you smell gas, do not reset anything: call the National Gas Emergency Service on 0800 111 999.

If your boiler is showing the most common of these codes, our step by step on the Worcester Bosch EA 227 fault goes further than we can here.

Worcester Bosch Greenstar 25i technical specifications

Every figure below comes from Worcester Bosch’s Greenstar i Combi ErP installation and servicing instructions and the ErP product datasheet for model 7733600012.

Alternatives to the Worcester Bosch Greenstar 25i

If you are replacing rather than repairing, the successors sit in Worcester Bosch’s current range, and their published guarantee lengths are a fair guide to how much boiler you are buying. The Greenstar 2000 is the entry level combi and carries a 7 year guarantee when a system filter is fitted. The Greenstar 4000 is the mid range option at 7 years as standard, 8 years with a qualifying Greenstar System Filter, and up to 10 years through an accredited installer or a loyalty payment. The Greenstar 8000+ range starts at 8 years and reaches 12.

Do not choose on guarantee alone. Match the hot water flow rate to the number of outlets you actually use at once, and have the incoming mains measured first. A larger boiler will not fix a weak water main.