Temperature drop on pump fed showers

[ZeroTools]

Hi all,

Looking for some advice on an issue with dropping water temperature on our showers. We have 2 thermostatic showers in the house, one in the main bathroom, one in the en-suite (both 1st floor - both Mira Elements). These are both boosted by a single pump in the airing cupboard (also first floor). Sometimes while using the shower there is a small but noticeable drop in pressure and then the water starts to run cold. Adjusting the temperature on the shower does nothing. This usually happens when one of us has a longer shower or we have guests stay (usually to the 2nd or 3rd person to take a shower gets a cold one), so initially we assumed we were just running out of hot water, as the pressure was still good and the pump was still operating. However I can get straight out of a cold shower and run the bathroom tap and get hot water, so it's not that. Initially we got around it by alternating between the 2 showers, or by leaving a break between showers, but lately we've stepped out of a hot shower in one room only to then get a cold shower in another. This seems to be pointing to the pump in my mind, but as it's a bit of a weird issue I would welcome advice before I spend the money having it replaced.

 

[Agile]

The problem needs to be diagnosed first.

That needs temperatures to be measured around the system.

I am wondering what you are using to measure the pressure!

Tony

 

[ZeroTools]

I am wondering what you are using to measure the pressure!

Mainly my face in the water...

 

[ZeroTools]

Joking aside - I can feel the pressure drop when I'm in the shower, immediately before it starts to get cold. I know the pump is still operating because the water still comes out at a fairly brisk rate, whereas it just dribbles out when the pump is switched off completely (also it is loud enough to hear it running).

 

[Agile]

Does the pump supply ALL hot outlets or just the two showers?

It could be that just the hot side of the shower pump is failing.

Sometimes the impeller can come loose on the shaft.

But that would be identified by a pressure GAUGE on the hot supply!

Tony

 

[ZeroTools]

The pump only supplies the 2 showers. The rest of the hot water outlets are gravity fed. Would a loose impeller be a repair or replacement job? I agree with you that it needs a proper diagnosis, I'm just trying to gather a few opinions that I can relay to the plumber.

 

[Agile]

Better to let a competent plumber diagnose the fault.

You don't say how old it is but presumably outside any guaranty period.

Most will only want to replace the whole pump.

Depending on what has gone wrong it MIGHT be possible to repair it. But you have not identified it.

You could ask the maker what might have gone wrong with it.

Tony

 

[ZeroTools]

Better to let a competent plumber diagnose the fault.

You don't say how old it is but presumably outside any guaranty period.

Agreed! But despite my best efforts to vet them, I may not end up with a competent plumber, so I always find it best to have some idea of what might be wrong before calling anyone else in (hence the question here). Just so I know what they should be doing in terms of investigation. I've only just moved in to the property so have no idea of the age of the pump unfortunately, no guarantee was left by the previous owner. Thanks for the advice, I'll pass it on.

 

[Madrab]

I'd be checking the filters to start with, it almost sounds as if something's loose within the hot feed and is restricting now and again. Then it's checking upstream of the pump to rule out supply problems. Then it's checking the pump and downstream.

 

[picasso]

Check the temp of the hot water going into the pump, absolute max should be 65c but around 60c would be better.

 

[ZeroTools]

Check the temp of the hot water going into the pump, absolute max should be 65c but around 60c would be better.

My boiler only seems to have the facility for me to adjust the CH/radiator temp, not the HW water temp, so I can't reduce the water temperature (it's a Glow worm flexicom 18hx). The shower pump has an auto-resetting thermotrip. Would this cause it to kill the hot water feed when it overheats? Might explain why it always runs cold after a similar amount of use then works fine again later on.

 

[picasso]

No thermostat on your hot water cylinder ?

 

[ZeroTools]

Aha! Yes, should have thought of that. It's set just below 50 degrees. I presume from your original comment that should be low enough for the pump (assuming the thermostat is working correctly - I haven't had any issues with scalding hot water from the taps)? The only reference to temperature I can see listed on the pump says: "Motor to BS5000 part 11 AMB 40 degrees C max".

 

[picasso]

I wonder if one of the non return valves has stuck open on one of the showers, that would allow the pumped cold into the hot supply, feel the hot water pipe coming out of the pump and see if it runs cold, if it stays hot as the shower runs cold good chance its the nrv/s

 

[RigidRaider]

We have the same setup as you and we had exactly the same problem, less dramatic but the showers would get slowly colder and we would be turning up the heat to try to compensate, yet the cylinder was still full of hot water.

The pump was sucking so vigorously that it was pulling cold water into the top of the cylinder from the cold water header tank through the cylinder overflow. Right now I'm struggling to visualise how that was happening but putting a hand on the cylinder overflow while someone was showering made me realise something was happening because it was freezing cold. We cured it by fitting a top cylinder outlet with a dip tube that goes deeper into the cylinder, somebody more experienced will come along soon and tell you what that's called.

This was after we had spent money changing the thermostat in our Mira shower valve, thinking it was dodgy.

You say the shower still runs slowly if you turn off the pump - so does it run hot for, say, ten minutes? Our problem only started when we fitted the booster pump.

Cylinder temp should be 60c, I believe.