Underfloor heating 1/4 turn valves not budging

Hi all - it's getting cold again so I wanted to turn my underfloor heating valve back on. It was installed 5 years ago and has never had an issue - its connected to a Viesmann system boiler and at the time I did not get any wireless control valve that would have meant I could turn the UF heating on and off to the downstairs diner/kitchen so I had a two zone system.

Today I was trying to move the 1/4 turn valves from the OFF to the ON position for the isolation valves that feed the hot in / cold return isolation valves and they are wiggling ever so slightly but not moving to the correct ON position. I don't recall it ever being an issue and it was last used less than 6 months ago and no one else has had a fiddle except when I turned them off.

Can I do anything else to identify the fault? Is there a risk it will leak if I remove the screw in the top position to inspect anything? Does the system need to be drained to replace these?

It's a pressurized unvented cylinder so I won't be doing much other than check the valves...

Neither is moving to the ON position and of course I don't have external rads only underfloor heating in the kitchen / diner...

1/4 turn valves can sometimes lock up, especially on CH systems, I've found that with mag filters sometime too. I'd use an adjustable to give a little more leverage and see if they give but I'd also be prepared to replace the valves if they snap.

TBH those ISO valves shouldn't really be used to isolate the UFH during the summer, it should be controlled at the flow valves but I do notice there are no manual or electrical actuators actually fitted to the valves.

I was not as savvy back then and when installed by a registered gas safe plumber but yes I think in hindsight isolating into zones with some device would be better but I was told manual means they should never stop working due to an issue (fat chance). Ok will see if I can leverage carefully - I don't suppose there is much chance of causing too much havoc (worst case replace and in the interim the valves would remain off).

@Madrab should I remove that screw inside to expose the spindle or leave it loose but connected to the twist lever and try to turn it with the wrench/spanner on that instead?

I don't know what that screw does, but I would say leave it.

Get a big adjustable spanner onto the end of the valve, and then try light tapping on the end of the spanner handle with a hammer. Don't apply force by hand otherwise you could break something.

Another thought is that heating the valve might help, but you'd have to do this in a safe manner. I'm thinking maybe pouring some hot water over it. I'm not sure about this though.

The screw just holds the plastic part of the handle to the spindle, if you remove it and take the handle off you may be lucky and find it's a square spindle in which case you can put your adjustable straight on it

Got it sorted - awkward access and put a cloth over the lever. The screw actually only held the lever over the spindle underneath but now I know not to close it off too often and keep it low (or just turn the temp down for the UF heating). Let's see how it goes. Thanks for the help in the forum!