Try this boiler for size: Debunking the big combi con


Installers have traditionally shunned fitting combi gas boilers in bigger homes, often associating the products with slow water heat up times and low flow rates.

However, this is now set to change, thanks to Navien’s new state-of-the-art NCB700 combi gas boiler.

Up to three showers at once

The game-changing NCB700 combi gas boiler is the first product of its type capable of delivering hot water to three bathrooms simultaneously. Thanks to a state-of-the-art flow adjustment valve and auto mixing valve, the NCB700 is able to provide lashings of hot water to three showers or baths at the same time, with no fluctuations in DHW temperature or flow rate.

Shattering all preconceptions of a combi boiler’s suitability for large properties, the NCB700 cleverly maximises recirculation of domestic hot water (DHW) to significantly reduce water wastage and offer flow rates up to an industry-leading 22 litres per minute (at 35°C temperature rise). Performance is further boosted by a turndown ratio of 15:1, ensuring water is heated extremely quickly, efficiently and economically, so a shower never runs cold!

Hot water on tap

Modern technology comes to the fore inside the NCB700, where a built-in recirculation pump ensures hot water is supplied to taps faster than if using a traditional combi boiler. This can be used in conjunction with the supplied NaviCircTM recirculation valve, which makes it even easier to set up a secondary hot water return system.

By installing the NaviCircTM beneath the furthest accessible fixture from the boiler, the valve then works in conjunction with the recirculation pump. The hot and cold water feeds are utilised to reduce waiting time at the taps, with circulation automatically blocked once the hot water temperature within the valve reaches 35°C – thereby saving a significant amount of water. This is something that simply isn’t possible with any other combi boiler or recirculation system!

Cylinders are history

Navien’s new energy-saving combi gas boiler can cope with the DHW and heating demands of larger properties with ease – rendering the system boiler and storage cylinder setup redundant. This is good news, as keeping water warm inside a bulky cylinder or scheduling it to preheat uses more gas and incurs a much higher operating cost for end users when compared to Navien’s NCB700 combi. Plus, removing or not installing a cylinder saves valuable space inside a property. The lack of a cylinder also eliminates waiting for water to heat up, with combi units supplying hot water whenever it is required.

Futureproof and hydrogen-ready

Navien’s NCB700 boilers are also hydrogen-ready, which is great from a sustainability standpoint, as they can operate using a mixture of 20% hydrogen and 80% natural gas. This ensures that once a hydrogen blend is introduced to the UK grid, there will be no need for any major heating or hot water system adjustments or upgrades.

The emergence of the NCB700 means combi boilers no longer have to be restricted by a property’s size. Indeed, Navien’s latest model is more than capable of providing lashings of hot water for larger homes. A new energy efficient and futureproof combi boiler crossover that prioritises DHW has now arrived – and it’s time for installers to embrace it.

Navien has a long-established history, having developed and manufactured boilers for over 40 years, while also leading the way in condensing technology for 34 years.

For more information about this and the company’s new high efficiency boilers, visit