Shower Pump

[Steevo123]

I'm having trouble getting my shower pump to kick in as if there's a negative head.

The cold water tank is in the roof, which feeds the hot water cylinder upstairs (i.e. below it). There is a shower pump on the floor of this level which feeds a shower and a basin.
Since having a new shower installed, the pump doesn't normally kick in. I used to find if you turn the valve temp down, then back up it would kick in but that doesn't seem to work now. The only knack I could find was to turn the shower on, turn the HW basin tap on, pump kicks in and then I can turn the tap off again to use the shower.
Since doing a quick Google I read I could try taking the shower head off the holder, and lowering it. Tried this and it kicked in fine by just turning on the "flow" control on the shower valve.

If the cold water tank was below the shower head I could understand this, but it makes no sense to me given it's plenty far above.

Can anyone advise please?

 

[Madrab]

What type of pump is it? It may be the flow sensor is getting tired or the filters may need cleaned and that is initially restricting the flow

 

[Steevo123]

It's a Bristan Varispeed SI 50.

I didn't realise they had filters in them. Could possibly be that - I'm in a hard water area.

 

[Madrab]

Yup, they sure do, isolate the water and take off the inlet pipe, inline filter should be in there.

 

[Steevo123]

Thanks. Opened up the inlet pipe this morning and turns out it was totally clear. Looks like that's not the cause of my problems.

 

[Madrab]

You need to check the shower flow rate with the shower head at its normal height with the pump off. Dropping the shower head is increasing the flow rate through the pump and triggering the flow switch. If the flow is above the pump activation threshold - 1.5 ltrs/min - then the reed flow switch for the pump may need attention/ replacing.