No cold water in shower

Hi all
We have a Methven mixer in an older shower which has suddenly decided that its not going to give us any cold water. If we take the cartridge out the cold water gushes out of the base no problem. So we purchased a new cartridge and guess what - still no (small dribble) of cold water :-(
Ideas?

Blockage on the cold side somehow.

Most shower mixers have two filters, one on the cold inlet and one on the hot. Old pipes corroding can shed lots of grit into the water.

Filters are now put in-line

Follow these steps to adjust your anti-scald device:

1. Take the handle or head off of your faucet.
2. If your faucet has an anti-scald device installed, it will most likely be the plastic device sitting directly under the faucet head.
Remember, though, that not all faucets have this device installed. So if you don’t see this plastic device, skip to the next section as this isn’t the reason you aren’t getting hot water.

3. Turn your anti-scald device to the right. Pull out the anti-scald device slightly to free it from the level it’s currently set to. Then, turn it slightly to the right and push it back in place.

4. Test the water temperature. If you notice that the water temperature gets slightly hotter than before, this was most likely your problem.

5. Repeat until the water temperature matches your needs. Continue making small right turns to the anti-scald device and testing the water after each adjustment. Once the water temperature is as hot as you’d like, replace the faucet head.

If your problem wasn’t the anti-scalding device, your shower mixing valve has most likely gone bad and is preventing hot water from mixing properly into your shower water.

you have to take cold feed of and inlet port has a filter in it

Thanks all - ok so there will be a filter on the feed into the mixer housing which is screwed to the wall (ie most of it is behind the shower lining?) I would have thought if this was the case we wouldn't get any cold out when the mixer cartridge was removed. (If we do this so only the housing is there in the wall and isolate the hot water, the cold hits the other side of the wall)

For clarity it is cold we don't have not hot - plenty of that :-)

We've now tried two new cartridges for the mixer (just in case we had lucked out and bought a faulty one).
So today we are going to replace the whole mixer and hope we don't have to destroy so much of the liner to get it in that it needs replacing too :-)

be aware that not all shower mixers are created equal, meaning that if you have low pressure hot and cold you are limited to what you can use, been there done that, I used methven units.

if on hot and cold low pressure remove the filters and throw over left shoulder.

Water won't just stop by itself. Something has to be blocked/damaged. Get a plumber as it might not be a problem with the mixer but something else in your pipework.