New logic + central heating issue

[thorn]

Any help would be greatly appreciated

Just fitted a logic + today to an old open vented system. All piped up and pipework changed etc, but when it calls for heat, it won't flow from the boiler and the temp goes sky high and then cuts out. The old boiler flow in the cylinder cupboard is connected to the heating flow and the return is capped. Flow and return at the new boiler are correct way round according to the old boiler. ISO valves are open and the rad valves as far as I can tell are bidirectional.

have never had this problem before - stumped

any help or ideas
thanks

 

[thorn]

The rads are filling and draining ok when I fill or drain the system, it is about 8m along the landing from the boiler to the cylinder cupboard so will check for any valves etc tomorrow. Hopefully it is the pump as had been mentioned a few times. Would hot water working prove that the pump is working?
thanks

 

[smtplumbing]

Check the pump was it a f5 fault I had this on the new logic I linked out the flow sensor on the flow linked it then bleed the pump then rocked it no hassle after th

 

[thorn]

Went back today, checked all the simple stuff like pump and valves, all working as I suspected. Took up a load of floorboards and found that the return I had capped, the old cylinder return didn't tee into anything, it just went straight back to the boiler. No idea how it worked before, basically I don't think it did and suspect the last guy in to change the cylinder, pump and 3 port had screwed up. Don't see that the heating can have worked in the state it was in. Ended up teeing some 22 into the 28 and hey presto job done!
Landlord Doesnt live locally and I think she has just brought the property so don't think she was aware it wasn't working

thanks for all the suggestions from everyone