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Bled one of the rads last night and now only some of them are coming on and even then only like warm. It’s an unvented system with an oil fired boiler, so nothing as simple as turning a couple of valves on the combi to get pressure back up.
Am I right in thinking it should still have expansion tank for heating loop even though it’s unvented system and that’s most likely where the problem is?
Off for an explore once I get home but trying to figure out where I should be looking first!
I would guess at an airlock somewhere, which will probably pass.
Can you turn the pump up to full speed, that's what I do when ours has one (normally after draining / refilling).
Surely if its UNvented then there would be a filling loop as how else can water get in to replace the air you've removed.
If its vented then air lock or the header tank is empty perhaps?
My simplistic understanding of unvented systems is that the supply (i.e. water in from stopcock, through cylinder out of taps) is unvented. My assumption is that the heating loop (closed loop through boiler / rads and heating loop in cylinder) must be vented with a header tank somewhere. I may be confusing two types of system though!!
Problem is I can't find either an expansion tank or a filling loop 🙁
Based on your understanding of unvented systems get a central heating plumber in.
Read the other central heating thread for an salutary tale
Mystery potentially solved - found the expansion tank (don't ask - 4 different loft spaces, none of which are linked!). Header tank was full-ish but topped it up, plus re-bled all the radiators and we now seem to have some heating downstairs. I'll let that run a bit and then try the upstairs circuit separately in a bit!
big_n_daft
Free Member
Based on your understanding of unvented systems get a central heating plumber in.
It's not an unvented heating loop - my understanding was correct - traditional vented heating circuit through the boiler to warm the hot water in the tank and water in radiators. The feed side of things in unvented and no intention of playing with that.