No heating to one zone

[Bushman]

So I have a vaillant combi boiler.

2 zones with a valve each controlled by Nest system.

When my Nest calls for heat zone one opens up and I have hot flow to manifold, pipes thus hot radiators.

When the other Nest calls for heat zone 2 valve opens up hot flow to manifold but no hot radiators.

I’ve bled all radiators in affected zone no air, I’ve tried closing all them off leaving one radiator on. Still the same... can’t think of what to do next. The system worked perfectly up until Friday.

I’ve been in the flat 2 years and drained the system twice, refilled and used inhibitor. The water was clear each time.

 

[Bushman]

Ok update, the radiator I’ve left on has slight bit of heat now I wouldn’t call it hot as before it was nice and toasty.

 

[Last Plumber]

Does it work if both zones are calling for heat ?
IS the 2 zone valve definitely opening?

 

[Bushman]

I tried having both zone valves calling for heat and only zone 1 works as it should.

I’ve had problems with these zone valves before but I believe it’s open this time. The pipework before and after the valve is hot even going to the manifold before it branches off to each rad, normally if the valve is closed these are cold to touch.

 

[neilrj]

Push the 'iffy' zone valve lever over to the manual position and see what happens?

 

[king of pipes]

Has to be the 2port valve ? manually lock it open .

 

[Bushman]

Since I have heat after the zone valve I would assume it’s open maybe just not fully.

Ok so my plan is to change the zone valves with Honeywell motorised valves in the next few days.

The original installer used a caleffi thermo zone vale commonly used for UFH, it’s just not realiable!

Only problem is it’s 3/4 so will need to fiddle about to get a 22mm one to work as I can’t find 3/4 Honeywell zone valve for looking.

I’ll report back my findings.

 

[Bushman]

Thanks all for the input, it was the zone valve. Replaced now working fine slight weep from a fitting but need to part drain the system again and it’s too cold now. Just need find a local supplier of loctite 577 to guarantee no more leaks. Wish I just used it from the start.