Things are not always what they seem! I had this problem only to find that it was not condensation - it was a leak, and was easily solved.
Though the original post is very old, people will still google the problem, so I'm posting what I did.
5-minute, easy temporary solution:
- Place plastic sandwich/takeaway tray under cistern – large one if going away.
- Wipe cistern at night with cloth (if indeed condensation is the problem)
For diagnosis:
- Wipe the cistern dry at night and see if it cures the problem.
- Wrap kitchen paper or toilet paper around all pipes going into & out of the toilet, securing with sellotape. Check later for any dampness.
When I did the above diagnosis, I discovered that the former did not cure the problem, and the latter showed that I had a leak from where the overflow pipe exits the base of the cistern. All I needed to do was to replace the washer.
Solution was simple (and I am awful at DIY):
- Turn off water at mains.
- Flush toilet.
- Remove top of cistern to access the internals.
- Lie thin piece of wood or similar along cistern, raise ballcock and use garden wire to tie the two together. (This stops cistern from refilling when water is turned back on).
- Turn on mains water (simply because I didn't want it off for any longer than necessary, for convenience).
- Siphon water out of cistern (into bath or toilet). Or remove with sponge but that is a pain in the neck - like being a gynaecologist (no room), & sponge drips everywhere. Siphoning got 90% out within minutes.
- Mop up remainder of water inside cistern with sponge; then kitchen paper to make it completely dry.
Now to take apart the overflow piping:
- Unscrew plastic nuts that hold together overflow piping (underneath the cistern). (I had to do this to get piping inside cistern out).
- Unscrew plastic nut where plastic piping attaches to base of cistern.
- Now you can go into the cistern and remove the overflow pipe along with the washer
- Replace washer
I was advised to add silicone sealant to the washer. I didn't and it worked fine.
Reverse to assemble. Do not overtighten nuts – you don’t want to strip the thread. Better to be conservative and keep a close eye on the join when you fill the cistern.
If you aren't familiar with siphoning:
- There is no need to suck or put anything in your mouth! Use a piece of hosepipe or tubing. Immerse tube in water (e.g. in basin or bath) so tube fills with water. Put thumb over both ends; now place one end in cistern & other in the receptacle (bath/bucket/toilet basin etc).
- For the siphon to work, the receptacle end MUST be lower than the end in the cistern. I.e. the net flow of water must be downhill - water will travel uphill providing the overall movement is downhill.
- Remove thumbs.
An alternative to immersing tube in bath (to fill it) is:
- Place length of hose beneath tap and let water simply fall into it (no need to stuff it against tap). When water exits hose, seal that exit with thumb & wait for other (higher) end to overflow. When it does, seal that end too with thumb. You now have a tube filled with water, ready to act as a siphon.
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That’s what I did and it cured a major problem.
I put the plastic tub back beneath the cistern, and put kitchen paper back around the pipes, to avoid being cocky – there was no guarantee that I had solved them problem. The kitchen paper got damp (heart sank) but it turned out to be from the condensation on the cistern. I now wipe the cistern with a cloth before I go to bed - never had the problem since.
If you found this post useful, please say so – it will encourage me to write posts more often.
