I have a Thermflow Thermal system, run by an ideal boiler. Today, I had to
drain down the system in order to replace two radiators with towel
radiators, and replace a small radiator with a slightly larger one.
I drained down, replaced associated fittings, and refilled the system. The
hot water is fine, however, for some strange reason, when only the heating
is powered on, the boiler will not fire up, and theres no error code
showing, only a "0" so I assume that its not even attempting to fire up. I
have heated the hot water up, and I can't for the life of me understand,
with both heating and hot water on, the radiators are heating up perfectly.
The room stat is to its highest setting, and by the point of the "click".
But still no "Call for heat" is happening with the heating.
Could your boiler perhaps fail to start if the water pressure is low? Is
your system fully bled of air? My pump is at a local 'high' point and had
to be bled by loosening the big bleed screw on the top. If I did it whilst
stationary it just didn't let enough out - only whilst the pump was running.
When the fizzling stopped I closed it again and the heating sprang to life.
Of course, you may need to bleed at a different point.