Hot water/mixer tap/worcester boiler

[Pdoff]

I live in rented accommodation. The housing association have put in a new bathroom and recently a new boiler. I have a mixer tap with shower head on the bath which I use for a shower rather than filling the bath. Since the new boiler was fitted the mixer for the shower kept cutting out the hot water once the cold was added. Either freeze to death or get boiled alive. I called the company out to check it. I was told nothing wrong with boiler, it is the mixer shower?????. The engineer turned the hot water down on the boiler so I no longer need to add cold water when using the shower. This is ok except when I want to wash dishes etc, the water is then not hot enough.
I called worcester today who confirm it is the mixer tap. I have called the housing association who are sending the plumber back out. My question is, what can be done to sort this problem out. I want to get my facts straight before the plumber comes as I don't want to be fobbed off. The mixer worked fine before the new boiler. TIA

 

[muggles]

Why have you assumed you'll be fobbed off?

You've not given details of your previous system so it's a little difficult to suggest the reason for the change in behaviour from your old system, but I'd agree it's almost certainly your mixer tap causing the issue. A check valve on the hot supply to the tap will probably sort it

 

[dilalio]

If the HA did your bathroom, then did your boiler, then they are responsible for your whole plumbing system, no?
They need to adjust the plumbing or replace the mixer so that it is suitable for the new boiler.