Aqualisa shower pump to combi conversion

[Argonman]

Hi. I’ve recently converted from a vented central heating system to a combi boiler.

I had an aqualisa pumped shower fitted on the vented system. This requires converting so it will work with the combi.

Aqualisa want to sell me a replacement processor (mixer unit) for a few hundred quid. There’s a bloke online who will convert to combi use for about £100.

Being a bit tight, I always tend to think that if something is possible, there is little reason why i cant do it myself. So………


The original unit comprises of a mixer unit which controls the hot & cold water inlet via stepper motor valves. The resulting mixture is fed to the on board pump and then to a single outlet to the shower. The unit is normally sited remotely in the loft and is controlled by switches in the bathroom.

The original unit compared to a combi only unit appears identical except that the combi unit is missing a pump & housing.

So i removed the pump and physically cut away the pump housing. The outlet to the pump became my shower connection

The electronics in the old unit allow you to switch over to combi boiler mode. So that’s what i’ve done.

Re-installed the adapted unit and all is well apart from an unusual quirk. When switching off the shower it stops totally then momentarily gives a short burst of hot water, perhaps 3 seconds then close down fully.

Any ideas?

Thanks. Chris

 

[Argonman]

A couple of example photos of pumped unit (top photo) and non pumped. My own now looks like the non pumped unit following my modification.

 

[Argonman]

For those who might want to carry out this modification………

Follow up. Problem solved.
The prospect of being unexpectedly hit with a jet of hot water once the shower was turned off worried me.
So to reduce the risk i turned down the DHW temperature at the boiler to 45 degrees on the basis that a squirt at this temperature carried minimal risk. I then carried out a reset of the shower by slowly moving through the whole range of temperature adjustment within the shower enclosure. Going from fully cold to fully hot and back again. I switched off the shower and no more unexpected additional bursts.

I can’t be sure if it was the temperature reduction or the reset procedure that solved the issue. But it's working well at the moment.

l’ll follow up in the future and indicate the reliability of the mod.

Chris

 

[gaz1]

wait until winter when your wanting more heat on the shower you may fond the issue comes back again due to the higher heat needed from the boiler

you should reduce the heat from the boiler anyway as it will make light duty taking cold water and mixing it before the shower

on the corvec britony it was turn the water temp lower to get a shower and have a non return valve on the hot side so when you mixed with cold it didnt back the hot side

but it depends on the water cold pressure to the property

not all boilers like people using mixers as the boiler is known to shut down due to lower pressure going through the boiler as sometimes you can end up with a cold shower then it gets heated again and back to cold again