Thermostatic Shower on a combi?

[rodders]

Can you fit a thermostatic shower on a system with a combi? I thought I has read somewhere that this is not advised as the combi will modulate the hot water and the thermostat will adjust the flow to suit the temperture. This means they will be fighting each other for control?

Also think that the shower is fed mains hot (from combi) and cold from CWSC. The shower is only luke warm and eventually will shut off totally with no water flow. They has been advised before that the ball valve in the CWSC might be sticking, but its not effecting anything else in the property?

Cheers

 

[SimonJohns]

I've never had a problem with this set up

 

[dancinplumba]

just wondering why you have cwsc when you have a combi ?

 

[johnnyboyoy]

you're always best off fitting a thermostatic shower with a combi. the combi wont modulate in DHW mode unless you're turning the open/close on the shower from low to high constantly. it only knows you want hot water at an outlet at a certain rate. Your DHW temp is set at the control on the boiler. The thermostatic valve will then mix what water it has to the temperature you've turned it to. However the best ratio thermostatic valves do is 5:1 i think. You'll prob get away with the imbalance due to the fact that the cold is fed from CWSC but best off pulling the tank out and just link in to out.

 

[scotty plumber]

i always thought that both had to be either mains c/w and hot fed from combi or both storage? Not one of each?

 

[johnnyboyoy]

when conversions get done properly yes - i did a combi swap a couple of months ago and he was complaining about pressure in the bathroom. luckily the house was quiet and i could hear something filling above my head when i ran the bathroom colds. probably would have been wandering around scratching my head for a while otherwise!

 

[tamz]

Best practice is to fit a pressure equalising valve (aka balancing valve) to showers fed from a combi.

The shower is only luke warm and eventually will shut off totally with no water flow.

This suggests the pressure differential between the mains fed (combi) hot and tank fed cold is greater than the shower is able to cope with.
Thermostatic showers will close down completely if they think there is no cold flow.

2 possible solutions.
Get the bathroom cold changed to the mains (easy unless certain flat types) which is the best solution or at a push fit a pressure reducer on the hot to the shower.

 

[PlumbBobBob]

i agree with all the above the hot and cold feeds to the shower need to be balanced for it to operate correctly. should be fairly easy to do if there is access to the pipework.