how can we fix boiler potterton netaheat 16-22 not igniting?

To check your boiler
switch your programmer on and your on dial at front to max
You should hear a small click this is the relay switch which makes 3 connections one being the fan.
If you do not hear the small click could be fault relay switch or its connections
You should now hear the fan if the relay works.
If no fan or click could be the internal fuse. Check. If ok
Check the fan by testing the terminals behind the bottom front cover. You don’t want to buy a new one if its not needed ( cost about £100 new )
You need a small amount of electrical knowledge to do this.
When the fan is working it causes a pressure plate to close which complete a circuit which in turn causes the spark generator to produce the spark which you can hear. So if you have no spark it could be the pressure plate or the spark generator. Check by using a circuit tester. If you hear the spark but the pilot light does not come on it could be that the pilot light is blocked or the spark is not close enough and needs adjusting.
If the pilot lights but the main burners do not fire then you need a new gas valve or it could be your mercury vapour switch which is plugged into the back of the gas valve.

Geoff but not Geoff the gasman
February 2007

This boiler has issues concerning carbon monoxide leakage due to ignition causing the case to buckle and should be checked over by a Corgi registered engineer, Please do not tamper with the boiler but the following maybe of help
The sequence of events are as follows.
Make sure that programmer are set to constant and room stat is on max.
Is the Fan Running - if Ok - If not then new fan
Is the a spark visable through site glass - If not New Pcb.
If Spark is Visable - New Gas valve.
The boiler is all but obsolete and spares are now very exspensive.

Geoff the gasman
February 2007