Mortice Deadlock keys will not turn bolt

[BigAl2]

I have a Union 3G114E 5-Lever Mortice Deadlock C-Series 80mm case in the front door of a tenanted flat. The lock was new in 2014, and supplied with three keys, one of which I kept.
The tenant has not been using this deadlock (I'm not sure why), and now none of the three keys will turn the bolt. Each key fits into the keyhole on both sides, and will turn a small amount, but the bolt fails to emerge, and stays flush with the front plate.
Do you think the lock just needs WD40 or similar, or is there more to the problem than this?

 

[JohnD]

I am familiar with this lock. It is a very sturdy and reliable model. It is very unlikely to have failed. As yours is the "E" version it is not very old.

What you describe will happen if the lock (or its levers) have been changed so the key does not fit (also if you are using the wrong key).

If you are handy you can take it out of the door and open the cover, you can see if the key lifts the levers the correct amount. The wrong key won't. It's possible (but very unlikely) that the grease on the levers had stiffened through lack of use. I have never seen it happen.

It is possible to buy a new set of levers with key, I don't know if it is worth your while tinkering with it.

A new one will cost in the region of £40.

Second-hand ones are on Ebay, but the 80mm size is uncommon (mostly found on older fire doors) and the older 3G114 (without the "E" suffix) does not meet the latest British Standard as the bolt is smaller, so will not satisfy your insurers. The "E" version has a larger bolt with a 20mm throw.

Replacement lever sets for the 3G114 will not fit the 3G114E as the travel is greater in the newer version. You may see it branded Chubb, Union, or Assa Abloy, due to a takeover. It is not quite the same size as current red-cased Union locks, so they may need some chisel or drill work on the door to enlarge the keyhole.

Edit
I see one on Ebay today at £20

 

[BigAl2]

Thanks John.
I fitted the lock myself, to replace an older one, and it was working in April 2014. Since then I'm pretty sure the young lady tenant has not tampered with it, and nor has anyone else.
I will remove the lock and its cover, and check the levers with a key as you suggest. Maybe the whole thing has just gummed up over time.

 

[JohnD]

scratch identifiers (1, 2, 3 etc) on the levers in the order you take them out (marker will not work as they will be oily)

You might find factory numbers stamped on them, which you can write on the inside of the case lid.

and photograph the arrangement of the parts before dissassembly.

 

[BigAl2]

Many thanks John. Very helpful.

 

[BigAl2]

I removed the lock from the door this weekend, opened up the cover and sprayed a little WD40 on to the moving parts.
After replacing the cover, I tried one of the keys and it turned the lock first time. All three keys now turn the lock from both sides.
Problem solved.