Hello pringle 35.. I am a Corgi Registered Gas Installer, a lecturer in Gas and Plumbing, and a quality assurance assessor of British Gas engineers.
Do not under any circumstances do what you have asked in your question.
Back boilers must under no circumstances be used without the correct fire front attached.
The results of panelling the fire could lead to incomplete combustion resulting in 1. Sooting up of the heat exchanger. 2. Copious amounts of carbon monoxide. 3. Flames licking out of the combustion chamber causing damage to wiring.
Current gas regulations prohibit the use of a back boiler in the way you describe.
You have made me very nervous.. I hope you do not live within explosion range of my place if you do decide to go ahead!!
Your best course of action would be to dispose of the back boiler completely and fit either a conventional boiler connected to existing hot water and heating systems, or go for a combi boiler which would enable you to get rid of all your storage tanks.. and be much more efficient anyway.. New condensing boilers can be as much as 98% efficient.. New model back boilers 75%.. older model back boilers in the region of 65%
If you want to know any more, you are welcome to email me at [Email address removed as per site policy. - AB Editor]
Best wishes
Norm