Old mixer shower with new Combi

[Entwisi]

Hi, We have recently had a new combi boiler fitted to replace an old boiler/hot water tank system. Unfortunately, the plumber forgot to tell us that our old shower(Mira Mixer) would not work due to the boiler giving too much pressure? Is there a valve I could get fitted in the shower supply that would allow us to use the old shower? I have seen the following

) but I'm not sure if they would do what I need. The plumber is not being very helpful so any help from here would be brilliant.

TIA

-- Entwisi

[Christian McArdle]

Mixers prefer both supplies to be at the same pressure. When the combi was installed, the gravity cold water supplies should have been converted to mains pressure. This should mean that the mixer valve would work anyway, provided it (and the hose and showerhead) could cope with the higher pressure and the flow rate is kept down below the combi's capability. They normally can cope.

Christian.

[Entwisi]

So all we need to do is reconnect it? Would it hurt to put a couple of those valves inline to drop the pressure a little? (The cold water was changed to mains pressure btw)

Cheers

Ian

[Christian McArdle]

No. Feed the mixer with full pressure. However, to comply with the law, you need to one of two things:

1. Attach the shower hose to the riser bar so that the shower head can't dangle into the shower tray or bath.
2. Install double check valves on the supply to the mixer.

This is to prevent the mains water system being contaminated with your bath water.

If the flow through the shower exceeds the capacity of the combi boiler and goes a bit tepid, then turn down the isolation valves a little to prevent this.

Christian.

[Entwisi]

Many thanks

[IMM]

1&st2=-87292365&st3=74789667&CATID=47&ObjectGroup_ID=263 ) but I'm not sure

Get the model number of the Mira mixer. Ring Mira, email them, and see if a high pressure cartridge is available. Most quality mixers, and Mira is one, had a low and high pressure versions of the same model. The cartridges are not cheap at around £100. Ask them if integral non-return vales are fitted in the mixer. If not then insert one in each of the hot and cold supplies to the mixer