combi boiler question

The combi won't fire up. It can be done by looping the heating F & returns together and then pressurisng, but impracticable for a temporary fix.

thats odd. water has stopped coming from the drain valve but the boiler still fires up for hot water ???

i have only run it for a few seconds so hopefully no damage done....

I believe they mostly have a water to water heat exchanger. The primary side is the CH water.

What is the shortest loop allowed ? I wondered why this is not done as standard, but I suppose it would required a few valves to change over from the normal CH to the loop. Simon.

If the boiler has a bypass circuit, then it can be as short as you like.

Check the boiler installation instructions. Sometimes a meter or two.

IME, installers are not looking to minimise disruption if something goes wrong. That's certainly something I did consider when DIYing my own (although I don't have a combi so this particuler feature is not relevant, but I can isolate and drain down sections of my heating whilst keeping the rest running).