The value everyone is switching to
The world's fourth-largest boiler maker, a stainless steel heat exchanger on every model, and up to twelve years of warranty — for less than the badge brands charge.
Ten models — seven combis and three system boilers — fitted at a fixed price with no survey.
At a glance
Navien split into three combi families and one system family. The NCB300 is the entry boiler, the NCB500 is the compact all-rounder, the NCB700 does things almost no other combi will do, and the systems keep your cylinder.
The highest hot water output of any boiler on this site, and the reason a large house can consider going without a cylinder at all.
The widest spread of any make we fit, every figure at a 35°C rise. The entry NCB300 starts where a lot of value ranges finish, and the NCB700 finishes where nothing else on this site reaches.
Parts and labour. Five years on the entry NCB300, ten on the NCB500, twelve on the NCB700 — and every one of them conditional on the boiler being serviced each year from the install date, which is Navien's own published condition.
Navien is one of the largest boiler manufacturers in the world. The UK arm runs its own technical and warranty operation from Guildford.
Three combi families and one system family. The NCB300 is the entry model, the NCB500 shares its compact case with more hot water and twice the warranty, and the NCB700 is the larger, higher-output one.
Hot water is kept primed in the pipe run, so it arrives at the tap almost immediately rather than after a wait.
Model by model
The cabinet sizes are the point with this make, so every drawing is the real height and width against the same reference outline. The 680mm NCB300 and NCB500 case is genuinely shorter than anything else on this site.
A note on the kW number. On a combi, the kilowatt figure in the name is the hot water output — that is the industry convention and it is the bigger of the two numbers. The heating output, which is what actually feeds your radiators, is lower. Where the maker publishes both we have printed both. On a system boiler there is no hot water output at all, because the cylinder does that job, so the kW figure is the heating output.
Navien's entry boiler, and the cheapest thing we fit. The same 680mm cabinet and stainless steel heat exchanger as the NCB500 above it — what you give up is hot water and five years of warranty, not build.
This is the entry point of the whole site, and it is worth being clear about what makes it cheaper. It is not the heat exchanger — that is the same stainless steel as the rest of the range — and it is not the cabinet, which is the same 680mm case as the NCB500. It is hot water and warranty: 11.5 litres a minute rather than 12.3 and up, and Navien's five-year term rather than ten. For a flat or a one-bathroom house that is often exactly the right trade.
The compact all-rounder. 395mm wide, so it goes in a standard kitchen cupboard, with a stainless heat exchanger and a ten-year parts and labour warranty.
The height is what does the work here. At 680mm this is the shortest cabinet on any of these three pages, which is the difference between fitting under an existing wall unit and re-planning the kitchen around the boiler.
Same cupboard-friendly case, a little more hot water. The sensible pick for a one-bathroom house that wants a bath filled quickly.
Two showers rated. Where a 30kW combi would start to disappoint, this one holds its temperature.
The top of the NCB500 range - two showers and a tap. More hot water than most 35kW combis from other makers, in a smaller box.
The crossover. Built-in recirculation pump so hot water arrives at the tap almost immediately, and a twelve-year warranty.
The recirculation pump is the feature worth understanding. Navien call it NaviCirc. Instead of the hot water starting its journey when you open the tap, the boiler keeps the run primed, so a long pipe run to an upstairs bathroom stops being a thirty-second wait.
Three showers at once from a combi, which almost nothing else on the market will do. For a big house that does not want a cylinder.
This is the boiler that lets a large house skip the cylinder entirely. Nothing else on this site will supply three simultaneous showers without stored hot water.
The small system boiler that replaces a tired 18kW - compact enough for an airing cupboard, with a ten-year warranty.
Mid-range system boiler for a three or four bedroom house running a cylinder.
The largest NCB500 system, for bigger radiator circuits and a high-recovery cylinder.
So which one? The NCB300 28K is the cheapest boiler we fit and the honest answer for a small flat or a one-bathroom house that wants the job done properly for the least money — the trade-off is five years of warranty rather than ten, not a cheaper build. Above it, the NCB500 32k is the sweet spot for a one-bathroom house: 13.1 litres a minute out of the same small case. For two bathrooms, the 37k or the 41k will hold their temperature where a 30kW combi from another make would start to disappoint. The NCB700 models are for large houses that have decided against a cylinder: the 54K is the only boiler on this site that will genuinely run three showers at once. If you are keeping your cylinder, the system boilers are sized 18, 24 and 30kW and the right one is decided by your radiator circuit, not by your bathrooms.
Side by side
The same figures as the blocks above, in a form you can scan. Prices are for a straight swap in the same position, including VAT, flue, filter, flush, thermostat and taking the old one away.
| Model | Type | Hot water | Heating | l/min | Warranty | H x W x D | Fitted |
|---|---|---|---|---|---|---|---|
| NCB300 28K | Combi | 28kW | 24kW | 11.5 | 5 yr | 395 x 285 x 680mm | £1,695 |
| NCB500 ON 30k | Combi | 30kW | 24kW | 12.3 | 10 yr | 395 x 285 x 680mm | £2,195 |
| NCB500 ON 32k | Combi | 32kW | 26kW | 13.1 | 10 yr | 395 x 285 x 680mm | £2,245 |
| NCB500 ON 37K | Combi | 37kW | 26kW | 15.2 | 10 yr | 395 x 285 x 680mm | £2,395 |
| NCB500 ON 41K | Combi | 41kW | 26kW | 16.8 | 10 yr | 395 x 285 x 680mm | £2,545 |
| NCB700 ON 42K | Combi | 42kW | 34kW | 17.2 | 12 yr | 440 x 353 x 695mm | £2,945 |
| NCB700 ON 54K | Combi | 54kW | 34kW | 22.1 | 12 yr | 440 x 353 x 695mm | £3,195 |
| NCB500 System 18k | System | — | 18kW | — | 10 yr | 395 x 283 x 680mm | £2,345 |
| NCB500 System 24k | System | — | 24kW | — | 10 yr | 395 x 283 x 680mm | £2,445 |
| NCB500 System 30k | System | — | 30kW | — | 10 yr | 395 x 283 x 680mm | £2,545 |
Every specification here is Navien UK's own published figure, re-checked against navien.co.uk and Navien's own NCB brochure on 19 August 2026. Hot water flow rates are quoted at a 35°C temperature rise throughout; Navien also publish figures at 25°C and 45°C, and the number means nothing without the rise. Warranty length is not the same across the range: Navien publish ten years on the NCB500, twelve on the NCB700 and five on the NCB300, which is their entry model. Every one of them is conditional — Navien state that all warranty lengths depend on an annual service from the installation date, and registration has to be done at the time of the install. We do the registration. Prices include VAT at 20%.
Navien build more boilers than almost anyone on earth and put a stainless steel heat exchanger in every single one, including the cheapest. On most other makes that is a flagship-only part. It is the component that decides whether a boiler reaches fifteen years, and it is the main reason the price difference is not a warning sign.
395mm wide, 285mm deep and 680mm tall. That last figure is the one that matters: it is the shortest cabinet on this site, which on a swap where the old boiler is boxed in under a wall unit can be the difference between a one-day job and a kitchen alteration.
Three showers at once, from a combi, with a recirculation pump built in so the hot water is there almost as soon as you open the tap. If you have a big house and do not want a cylinder taking up a bedroom, this is the one boiler on our list that genuinely gets away with it.
Navien UK runs its own technical, service and warranty operation from Guildford, and publishes a warranty look-up so you can check the cover on a specific boiler yourself. Navien state that their boilers carry a guarantee of up to twelve years, which as with every make on the market is conditional on the boiler being serviced each year.
Every specification on this page is Navien UK's own published figure, re-checked on 19 August 2026 against navien.co.uk and Navien's own NCB brochure. This page used to carry a flagged exception — the NCB700 ON 42K flow rate, which Navien's product page does not publish at the 35°C rise used everywhere else, so it had been interpolated at 17.3 litres a minute. Navien do publish it, in the brochure: 17.2 litres a minute. The derived figure has been replaced with the published one, and the 54K corrected from 22.0 to Navien's 22.1. Every flow rate on this page is now a manufacturer figure at a 35°C rise.
Questions
It is a fair question and the honest answer is no, but the reason matters. Navien is one of the largest boiler manufacturers in the world and has been selling in the UK for years — what it does not have is decades of British brand recognition, which is a marketing gap rather than an engineering one.
The thing that would worry us is a make with no UK technical operation and no parts route. Navien runs both from Guildford.
Because it is how Navien build. On most makes a stainless exchanger is a flagship-only part and the value models get aluminium.
It is the component that most decides whether a boiler reaches fifteen years, so having it across the range is the main reason a lower price here is not the warning sign it would be elsewhere.
It is the hot water output. The NCB500 37K puts out 37kW to your taps and 26kW to your radiators, and Navien are one of the few makers who publish both figures per model rather than just the headline one.
That is why the 41K and the 37K show the same 26kW heating output. You are buying more hot water, not a bigger radiator circuit.
395mm wide, 285mm deep and 680mm tall. The height is the useful part — it is the shortest cabinet on this site, which is what usually decides whether a boiler clears the underside of a wall unit.
Clearances around the case still apply and they are what actually decide a legal position, so it is a good sign rather than a guarantee.
Because that is what Navien publish, and we are not going to write a longer number than the manufacturer will stand behind. The NCB300 is Navien's own entry model and it carries a five-year parts and labour warranty; the NCB500 carries ten and the NCB700 twelve.
What it is not is a cheaper build. The NCB300 has the same stainless steel heat exchanger and the same 395 x 285 x 680mm cabinet as the NCB500. The difference you are paying for further up the range is hot water and warranty length.
Whichever you choose, Navien's condition is the same: the warranty depends on the boiler being serviced every year from the installation date.
Navien's built-in recirculation, fitted to the NCB700 models. It keeps the hot water run primed so that hot water reaches the tap almost as soon as you open it, instead of after the usual wait while cold water clears the pipe.
It makes the most difference in a house where the bathroom is a long pipe run from the boiler.
Fifteen questions and we will size it, price it and tell you when we can fit it.
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