Lukewarm water from power shower

[calljim1]

Amateur looking for some help please.

I have two power showers, make unknown I'm afraid - they're inbuilt and were installed before I bought the property.

Cold water is fed to the Mira Enduro pump from the CW cistern in the loft, hot water is fed from the cylinder in the airing cupboard (where the pump is floor mounted).

We had a problem with our boiler so were without hot water and heating for 7 days until a new PCB was fitted last week. Since then, both showers have been lukewarm at best. Hot water to all other taps in the house is fine.

I have had the pump checked by a Mira engineer who confirms that the pump is running fine - hot water is going in and out. The hot water out pipe, which runs up into the ceiling is hot to the touch. The engineer suggested there may be an airblock somewhere between the pump and the showers.

I have removed both shower heads and dropped the showers hoses to floor level, running the showers on maximum heat. Water flow/pressure is fine. I get a couple of seconds of good, scalding hot water, then the flow goes lukewarm, although still with good pressure. Would an airblock cause this and, if so, how do I fix it? Having read an earlier post on the forum, I'm reluctant to force mains CW into either shower system.

I suppose it could be a problem with the thermostat, but it seems strange that both showers stopped working properly at the same time and the problem only occurred after the boiler was fixed.

Any suggestions would be greatly appreciated.

Thanks

 

[bengasman]

..The engineer suggested there may be an airblock somewhere between the pump and the showers.

The "engineer" is a muppet.

I suppose it could be a problem with the thermostat, ...

With a cylinder, one working hot water tap in the house proves the dhw is ok.

 

[calljim1]

Thanks for the response bengasman, but I'm still none the wiser.

You say that the "engineer" is a muppet, but not why. Do you reckon it's definitely not an air lock?

I agree that there's no problem with the cylinder's thermostat, but was thinking more along the lines of whether the fault lies with the thermostats in each of the shower units (unusual that they would both malfunction at the same time, but not impossible I suppose).

I'm really scratching my head over this one

 

[bengasman]

You say that the "engineer" is a muppet, but not why. Do you reckon it's definitely not an air lock?

Airlock of 0.3 bar resistance ( one floor's height ) is pretty high, piss poor pump will do 3 times that, good one 10 times.

 

[calljim1]

The Mira Enduro is a good one, so I'm led to believe.

So that leaves me with hot water either cooling rapidly somewhere between leaving the pump and exiting the shower, or too much cold water being pulled into the mix.

I have thought of turning off the isolation valve for the cold water feed into the pump, then running the shower(s) on maximum temp to see if hot water comes through, but I'm worried that this might damage the pump.

Worth a try or best to be avoided?