Our customer lives in Kent in a 1890s set of railway construction workers cottages.

Side of property in Kent

When the property was refurbished in 2004, he specified an Archie Kidd (Thermal) VHE Model 1 oil boiler. This was before the UK Government had latched onto condensing boilers being the future. In fact Archie Kidd had designed his Model 2 prototype in 1959 as part of his strive for energy to be conserved and not wasted needlessly.

The Kidd Model 1 should last in excess of 30 years, so it was a shame to remove this now discontinued British leader in the history of heating innovation.

Our customer, who in our view was a bit of an ignorant peasant getting rid of it, wanted space to site a garish fridge freezer where the boiler resided, and asked for a new boiler suitable for external positioning.

New Outside boiler location

The Navien LCB700 external model is a green cased highly insulated kerosene boiler (also able to run on diesel) using Blue Flame burner technology. Unlike all other UK domestic oil boilers, this unit is a single stainless steel design, built as a Blue Flame unit, rather than a converted existing orange flame model. It is untroubled by low heating water temperatures, such as those produced by underfloor heating and low temperature radiator systems.

During the installation of this particular LCB700, we wanted to see if we could add weather compensation to the radiator system. This is not a new phenomenon, and is particularly suited to gas condensing boilers because most of them have no minimum return water temperature. In contrast, oil boilers in the UK are all still predominantly made from mild steel like they have been since the 1950s – so would be damaged by internal corrosion if water was returned below their parameters for the non ferrous part.

Our customer had Evohome zoning, and this does have an optional relay module that communicates to boilers with OpenTherm. OpenTherm can work in some very clever ways, but Evohome does not transmit compensation data to alter the water temperature, so this was not used here.

Customer’s Evohome unit dating from 2012

Instead we found that the Navien had some low voltage connections that we could interface to Evohome, that would put the boiler in two different modes,

  • constant temperature (for hot water cylinder reheating)
  • variable temperature (for radiators)

A Navien weather sensor was added and some parameters changed in the LCD set up menu… and remarkably, the boiler was thereafter under control of Evohome, and switched between the two modes intelligently.

Navien LCB700 boiler controls. 23C outside today!

The Naiven boiler now works in low temperature mode most of the heating season, dynamically adjusting the flow temperatures in the background.

New Navien LCB700 system boiler with oil Tiger Loop and fire valve

The rooms have a less fierce more distributed temperature as a result, with no loss of comfort. The efficiencies in full condensing mode are the highest possible, and of course another tool in the LCB700 armoury is the two stage output; although this is a 28Kw boiler, it will automatically drop to 21Kw as appropriate.

Latest Grundfos low energy pump inside Navien system boiler
We mounted the grey weather sensor on the reverse of the boiler casing while we ascertained whether it would work the way we expected

Downsides? Some homeowners like scorching hot radiators and although the rooms still reach the same air temperatures as before, the effect is different. Superior in my opinion. With Evohome the warm up times of rooms is slightly slower.

This is one of the customer’s Vogel und Noot T6 ‘valveless’ centre tapped radiators with an early 2005 Honeywell HR80 wireless TRV (still working with Evohome)

So, what happened to the Archie Kidd boiler, as it was still in fine condition after 17 years of service?

Space vacated by old Archie Kidd boiler ready for fridge freezer. There was room for a MagnaClean 28XP system filter too!

It lives on! The owner has repurposed it in his barn workshop, by linking it to a fan coil (warm air blower) rescued via the ‘Bay of E’ from another decommissioned biomass plant, in Exeter. It will now warm his barn up from scratch in a few minutes, by wireless control of course.

Kidd boiler carrying out new duties

We can use weather compensation with Navien in conjunction with their gas, LPG and Oil boilers. It is possible to make Evohome zoning, and also unsophisticated single zone thermostat solutions such as Nest, Hive etc work in this way.

For the first time we can use a quality boiler and interface it to existing house heating and hot water systems, giving weather compensation benefits, without being tied to a boiler manufacturer’s bespoke unfathomable* controls.

*that refers to all the manufacturers of boilers. If you fit weather compensation keep the manual nearby.

As a footnote, unfortunately Navien UK have recently discontinued stocking their weather sensor accessory due to no installers using it, we hope they might reconsider! We can use a generic sensor in the meantime.

Lastly, I need to disclose to being the both the installer, and the end customer, for this case study.