KIDD VHE BOILERS – Useful information

Harwood and Associates were asked by Mr Anonymous to investigate the option of installing a Kidd Very High Efficiency oil fired boiler to replace the two original 40 year old wall-flame oil boilers. These boilers are manufactured by Archie Kidd (Thermal) Ltd, Poulshot, Devizes in Wiltshire.

As an alternative, we also looked at installing a Grant Vortex condensing boiler. This is a good quality typical domestic oil fired boiler comparable in the market place as the old wall-flame boilers were.

The Kidd boiler installation was approximately 20% more expensive but was considered to be a wiser investment taken over the next 3 to 4 decades due to the longevity of the Kidd boiler.

The efficiency of the boiler is down to two simple concepts; good thick insulation enclosing the entire boiler and an “economizer” (secondary heat exchanger) installed on top of the boiler and connected to the return pipework from the heating system. The flue gasses pass through this economiser as they leave the combustion chamber and deposit heat into the return water raising the water temperature before it enters the main boiler.

The action of the economizer reduces the flue gas temperatures to a point where they condensate resulting in the need for a small drain pipe to be run away from the boiler and flue installation.

The Kidd boiler is of a robust construction with a simple control system designed for a life expectancy of 30 to 40 years subject to good routine maintenance and professional installation.

Existing System:

The existing system consisted of two 40 year old wall-flame boilers sharing the same 9” brick flue.

The smaller 50,000 BTU boiler served two hot water cylinder gravity circuits.

The larger 100,000 BTU boiler  served three pumped heating circuits.

The only control on the system were two simple timeclocks.

New System:

The new installation is served by one Kidd Model 2,  29.3 to 47kw boiler on a fully pumped 54mm circuit in the boiler room.

The two gravity cylinder circuits were altered to pumped circuits and connected into the 54mm pipework along with the three heating circuits.

Isolating valves and motorised valves were installed on each circuit to provide easy maintenance in the future without draining down the whole system and fully automatic time and temperature control of each circuit.

A Fernox TF1 filter was installed on the 28mm return pipework just before the boiler to arrest the magnetite sludge and any un-wanted particles in the existing system. This filter is designed to be isolated, removed and cleaned very easily during the annual boiler service.


The existing chimney was lined with 5.1/2” heavy gauge aluminium rigid lengths of pipe and back filled with vermiculite insulation granules and topped off with a suitable rain-cap.

Installation of the flue was particularly difficult because of two “off-sets” in the length of the flue, one immediately above the boiler and the other at first floor level. This resulted in extensive building works in opening up the flue at first floor level and raising the “head” of the recess where the boiler was positioned. Special off-set flue components were fabricated to order by Kidd and supplied along with all the other flue products.


The condensate from the boiler is usually run to a nearby drain. In the case of this property the boiler room was internal with no suitable drainage nearby. The problem was over come by the installation of a fully automatic condensate pump installed next to the boiler. This unit pumps water vertically up a clear 15mm plastic tube to ceiling height where it connects to a 22mm p.v.c. pipe run with a fall through a high level boxing in the hall and passing through the external wall and connecting into a soil stack outside.

The live feed for the boiler and pump are controlled by the condensate pump and in the event of a condensate pump failure the supply to the burner and pump will be terminated.

Feed & Expansion:

A new 90 litre feed and expansion tank was installed in the loft with  new 22mm cold feed and 28mm open vent pipework as the old cold feed and vent pipework were in iron and corroded inside forming a blockage in the pipework.

The installation of the new boiler was carried out by Harwood and Associates Father and Son team Terry and Ben Harwood.

The building works was executed by local builder from Cowfold, Neil Ansell.

The installation and wiring of the new controls system was carried out by Steve Cresswell and Adam Spears of S&M Electrical from Partridge Green.

Scaffolding for access to the chimney was provided by local man Andy Bennett and his team from Partridge Green.


Kidd ceased trading a couple of years ago. However; if you need help with servicing or maintenance you can contact Baden Powell on 07703-428762 or email him at


“…it was indeed an interesting project, and we are extremely grateful to you and Ben for all your hard work in overcoming the various problems, and in finalising everything in your usual professional way. “

Mr Anonymous 5th October 2010