Heating hadn't been used in my house for a long time, before I moved in. Radiators didn't heat when pump running. One pipe to rads was extremely hot but rads were cold.
System is semi gravity from coal fire. DHW is gravity, with feed and vent pipes, and a drain off at the back boiler. Heating loop is pumped. Both flow and return pipes rise up from ground floor back boiler, into a cupboard in a first floor bedroom. Then they drop down and disappear under the floor. It then has microbore from the 22mm pipes to upstairs rads. More microbore drops down in the kitchen and tees off to two rads, and some goes down the side of the stairs, to the hall rad. No drain off on downstairs rads.
Having tried everything. I turned the pump around and rads began to work, albeit with a lot of noises, trickling and other air/water sounds. It's never run well. There's always a lot of air trapped in the pipework in the upstairs cupboard, where the pump is. I want to add an automatic air valve in the cupboard, but I want to fit it on the positive pressure side.
I can't go off where the pipes come off the boiler because it's behind an inset fire. I can't go off which way the rad valves went, because it was random. I can't go off which way the pump is for obvious reasons. When I moved in, the pump was trying to pump hot water from boiler to rads. I've had it pumping cold/warm water from rads to boiler for a couple of years, semi successfully.
Recently, I did a test. I got the fire going without turning the pump on. The pipe the pump is on got warm but not hot. The other pipe stayed cold.
My question, if anyone can help, is this: Is the pipe with the pump on it the flow, or the return? Am I currently pumping backwards to the boiler and it just won't work the other way, due to an air lock? Or, am I pumping the correct way, in pumping to the boiler, and the pipe with the pump on is the only one warming up when the pump's off, because of an air lock? Any help much appreciated.