Netaheat Blocked Air Restrictor

All versions of Netaheat have an air pressure switch. This is a safety device. It senses the air pressure produced by flue fan, and once the flue fan pressure has been sensed, it allows gas to pass to the pilot and the flame to light, followed by ignition of the main burner.

If the flue fan fails to run, it would be dangerous for the pilot flame to ignite so the air pressure switch prevents this happening, unless and until it detects the air pressure coming from the fan. 

In addition to this, the combustion chamber needs ventilating for a few seconds before any ignition to purge any residual gas, and this is the function of an air restrictor inserted into one of the thin tubes connected to the air pressure switch. It simply delays passage of air and pressure for a few seconds to allow time for the flue fan to purge the combustion chamber before the pilot flame ignites. 

This air restrictor is terribly prone to blocking and is responsible for any number of perfectly good Netaheat boilers being scrapped, simply because so few gas technicians realise it is there, and unblocking it would get the boiler working again! 

The location of the restrictor varies according to the exact model of Netaheat you have, but if you can find and recognise the air pressure switch, you will find two thin polythene air hoses connected to it. One of the hoses will have what looks at first sight like a simple brass joint inside it, and that is the (blocked) restrictor. The hose will be split at the restrictor so gently ease the hose from each end of the restrictor. Clean out the tiny hole through it, replace it and the boiler will probably work again. 

Here is a photo of a Netaheat MkIIF with the main cover removed (you don’t need to do this) and the lower control panel hinged down to reveal the location of the restrictor. In the red circle. Not the best of photos but its all I can find at the moment. 

Other versions of Netaheat will have the restrictor in slightly different positions but it always will be found in one of the thin hoses in this general area. 

There are two ways to clean out the hole through the restrictor. The hole is very small and can just be seen through if one holds it up to the light. I use a piece of high E electric guitar string. This fits through perfectly. Another way is to put half an inch of white vinegar into a saucepan, drop the restrictor into the vinegar and boil it on your hob or cooker for a few minutes. This dissolves the blockage and clears the hole very well too. 

I’ll post a photo of the restrictor itself shortly, once I’ve found one here to photograph!

Text me on 07866 766364 if you’d prefer me to come and do it for you. 

Mike