Peculiar central heating: upstairs hot, downstairs cold!

Just had my new combi boiler turned on for first time this evening after kind CORGI man turned on gas for me. Lots of lovely hot water, but my radiators are misbehaving. A bit of history:

I've been renovating this house, which has an old oil fired system still waiting to be ripped out. The old hot water tank is isolated, the two cisterns in the attic are isolated, and the central heating and hot water lines are now tapped into the new boiler.

When I bled the radiators, I opened one stopcock on the ground floor and managed to empty the entire system - perfectly normal. Refilled the system from the filling loop on new boiler, filled all radiators to 1.5 bar. This, one would think, shows that the radiators are all on the same system - perfectly normal. However, with the new boiler on, only the upstairs radiators are warming up

Checking the plumbing that runs from upstairs to downstairs (running past the old boiler) I can feel no increase in temperature, except for a slight warmth at the top of one of the pipes (presumably conduction?) but not at the bottom. No water is flowing downstairs.

I tried isolating all the upstairs radiators (except one which I kept open a crack) but the boiler simply couldn't pump the water round anymore. Seems to me the downstairs rad loop isn't seeing the flow from the new boiler. But given I filled the entire system from the filler loop at the new boiler, how can this suddenly be?

My thoughts, and I'm probably wrong: is there a check valve in the system somewhere preventing flow in the downstairs loop? If so, maybe I need to reverse the water flow to sort it out

Any plumbers out there that've seen this a million times before and can offer any advice?

rt18 said:

My thoughts, and I'm probably wrong: is there a check valve in the system somewhere preventing flow in the downstairs loop? If so, maybe I need to reverse the water flow to sort it out

Click to expand...

Sounds as though you could be correct, especially if it was an old gravity primary oil system.

Instead of reversing flow it would be best to find the anti gravity valve and remove it.

As I have no idea what a checkvalve/antigravity valve looks like, I took this photograph of something I've found that I can't identify. Is this the culprit perhaps? It sits in the vertical runs near the old boiler.



Zoom:

Yes, thats it. Remove it and possibly the gate valve lower down as well.

I take it this gate valve is fully open

Thanks Dave! I'll drain the system in the morning and get that sucker out. I take it turning it upside down would be stupid, so instead I'll make up a short stub of 22mm to bridge the gap.

Yes, the valve is certainly wide open!

Cheers again!

Forget this valve. At this age it could stick shut whatever way up it is