URGENT Hot water is cold. Boiler or valve

[TheCatWhoNeedsaHotShower]

Please advise me. I am a disabled pensioner. I had a wet room fitted just over a year ago using a local authority grant. Builder was employed by local authority. I had no say in who carried out the work.

I have called the builder out under the guarantee several times for water leaks. The shower has been changed 4 times. One of the leaks involved my ceiling which had to be repaired.

About a month ago I called the builder out again water was yet again coming out of the shower head when the shower was turned off. A bucket full an hour roughly. The water in the shower was running cold when I tried to have a shower.

Builder came last Wednesday and fitted a water limiting valve under the sink downstairs. The water is barely hot in the shower and the water pressure is very low in the basin.

I own my home. I paid a gas registered plumber on Thursday to service my combi boiler. All ok.

Have now noticed the hot water in the kitchen sink downstairs is running cold.
Is it the boiler or the water limiting valve causing problems?
What was the original problem with the shower? And how should it have been properly fixed?
Please help. Thank you