Mixer shower off combi boiler too hot

12 Oct 2009
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United Kingdom
I have a Vaillant combi bolier (ground floor) and recently had mixer taps installed for a shower (first floor). Before the mixer was installed I had really good cold water pressure to the bath and reasonable hot water pressure. Now the cold water pressure is poor and the hot water too much. The cold water tap has to be turned fully on and the hot water tap on slightly to get a remotely manageable temp and even then it is v. hot.

While running the shower I noticed that the cold water from the bathroom sink tap is now warm. When I used to run a bath with the hot tap on this never happened.

Does anyone know if the issue is likely to be the installation is incorrect or am I unlikely to be able to run a shower from my combi boiler without such issues...
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