Not enough Hot Water to shower

[Bobby19]

We have a thermostatic mixer shower in our ensuite, which is fed from a shower pump.

The problem we are having is that we are not getting enough hot water to the shower head. There is plenty of hot water in the system as we have it at the taps and another shower in the Main bathroom (Fed straight from the tank).

When we have put the immersion heater on, we get enough hot water to come through the shower.

We thought it may be the mixer valve, but how do we get the hot water through when the immersion heater is on?

I'd be grateful for any ideas anyone may have?

 

[JohnD]

do you mean the water goes cold, do you mean the water stops, do you mean the hot water stops and the cold continues, do you mean the water stops and air comes out?

Anyway, if you have a pump, it is probably sucking the hot water out of the cylinder too fast and the water level is dropping and it sucks air in.

You have got a cylinder, and a water tank, obviously?

How big is the cylinder?

When you squirt the shower into a bucket, and time how long iata takes to fill, how many litres per minute does it deliver?

 

[Bobby19]

The water temp rise from cold to a lukewarm and then maintains that temp. There is no problem with water supply, just the temperature.

We have a cylinder in the airing cupboard. Not sure of exact size but I'd call it a standard domestic size, from what I've had previously.

In terms of the water pressure it is good. I am not at home to measure the litres/minute.

Ta

 

[JohnD]

does the cold supply come from the tank, or is it mains pressure?

Verify that the mixer is not at "anti-scald" position (check the instructions)

It sounds possible that the mixer is not working properly, it might be mixing too much cold in. See if you can turn the service valve on the cold pipe off, or down. Make sure that any valves on the hot supply are fully open. See if the mixer gives the correct temperature when the pump is switched off or disconnected from the electrical supply

Apart from verifying that the mixer is working correctly, the most likely cause is that the pump is trying to suck from the cylinder more than it can supply. Go up to the cold tank, you should find a large copper pipe bent over it, that is the vent from the cylinder. See if that is sucking when the pump runs. You can put the end of the pipe into a mug of water. Look also at the supply pipe that runs from the bottom of the cold water tank and supplies the cylinder. See that it is not choked with limescale, insulation or drowned wildlife.