Aqualisa Shower stops pump

JohnD said:

Perhaps you have connected the hot and cold pipes the wrong way round.

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WaggleSax said:

Hi Forum,

Hoping for some confirmation here. I have an Aqualisa shower mix (609 chrome I think). Grundfos STR2 1.5 was replaced 10 months ago, now the pump cuts out when cold water is selected on the mixer. I'm confident this isn't airlocks or cold water feed issues, pump seems good too.
Could this be a faulty mixer cartridge stopping the call for cold water and causing the flow sensor in the pump to turn it off?

I let all the hot water get used up so only cold in the system and the shower continued to work regardless of mixer temp selection. Turned on the boiler to heat the water to tried again and the pump stopped again when cold water was selected.

Thanks for any advice,
Matt

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Johntheo5 said:

You have a positive head pump which requires a minimum flow both to start it and stop it, it probably has 2 flow switches, one on the hot and one on the cold, pump probably requires ~ 1 to 2LPM to start it. If you try and start it with the shower mixer to cold what is the flowrate (pump off) and does it then start but stops again?, compare this with the flowrate with the pump switched off and shower mixer to fully hot, might give some idea of where the problem is.

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WaggleSax said:

That was a good test @Johntheo5 I didn't consider testing with the pump off, I assumed that the water wouldn't be able to run.

With the pump off, cold and hot run well. I let the cold run for approx 1 min and then turned on the sink hot tap. As the tap warmed up the flow of water from the shower decreased, until it stopped completely. I reckon I was right and this points the finger at the bi-metal cartridge in the Aqualisa mixer.

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