Shower Pump only kicking in when water temperature is set to cold.

E

Eireog007

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Moved into a new house about 3 months ago and noticed that the shower pump wouldn’t kick in when the temperature dial was moved up above the cold end of the setting. This appeared to resolve itself with some rather unscientific push of buttons/switches by myself but now is happening again.
The hot water has been turned on by my heating controls in advance of trying to use the shower so there should be hot water available. There is the old immersion settings within the hot press separate to the 2 zone control panel downstairs which is left turned off.
Has anybody come across something like this before?
 
Can you post the model number of the pump or a photo, so we can tell if it’s meant to pump both the hot and cold?
 
It’s a Grundfos STP 3.0 B

It’s designed to supply both hot and cold and has worked for the last 3 months or so. The problem I outline above was there when we moved in and has resurfaced again in the last few days. I’m just trying to determine what’s causing it.
 
I'm only a DIYer so take this with a pinch of salt. But you'll see on your pump there's a sensor on each of the hot and cold sides of the pump to detect water flow, with the idea being that when you turn on your shower water will begin to flow (just because of the positive water pressure from your tank in the attic) through the pump, the sensors detect this initial flow and tell the pump to start. So in your case the things that could be wrong are that the flow sensor on the hot water side is faulty or the board on the pump that the sensors connect back to is faulty.

It could also be that there isn't enough positive water pressure from the hot water thank to begin the flow through the pump, if perhaps a valve were closed or partly closed, though you'd think if that were the case you'd also notice that the shower would not be getting enough hot water once you do get the pump running?

It looks like the flow sensor on your pump could potentially be replaced without going near the water in the pump as it seems to just strap onto the pipe, so may be achievable as a DIY electrician job (depending on your comfort with mains electricity). Though a decent plumber would probably have the tools to test if the sensor is the issue, whereas you'd have to just start buying parts and try them out.
 
There are usually gause filters in both the hot and cold inlets to the shower mixer valve. If these are partially clogged you will have low water flow. You should try and check these before doing anything else.
 
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