Shower disaster

[mike42]

Hi

We had a shower installed a couple of years ago and it has never performed as it should. I wonder if anyone would be kind enough to offer any advice or thoughts? (Apologies it took a fair few words to explain the problem).

The shower is fed from a CW tank in the loft with a much larger than normal HW cylinder - it is about 6ft tall and is in the airing cupboard. There is a shower pump (2.3 bar) next to the cylinder and the shower is on the same floor. The cylinder is vented and heated by an indirect coil fed from the boiler. I think its all pretty "old school" standard apart from the 50% or so larger cylinder. The pipes are 22m most of the way to the shower head and the HW pipe uses a dedicated flange that is situated at the very top of the cylinder. I never saw the exact route of those pipes and what the "plumber" did.

We set the heating and HW on the programmer to only come on in the evening - it is never on in the morning.

Showers in morning take about 1-2 minutes to reach full flow (that we could live with) and then perform fine afterwards. Showers in the evening when the tank has been recently reheated, are terrible with approximately 25%-50% of the flow achieved in the morning. It basically trickles out and now that the wife is expecting, I'm getting this in my ear on a regular basis. Nothing else is using any water anywhere in the house at these times. The other thing to add is it does seem to be worse in colder weather.

I'm thinking it has something to do with air because is there was some kind of blockage wouldn't it be constant? The "plumber" that did the original job certainly left a million black plastic shavings in the cold tank when he'd finished. I'm wondering if its possible that when the HW tank heats up and isn't give hours to settle, then maybe air bubbles form on the coil or something and thats why the pump never settles down? If that was the case, then fitting a flange on the side of tank wouldn't help? These are only my guesses though and would they account for such a dramatic reduction in flow?

In the past I have inspected the mixer and taken the connections off the pump and inspected and there wasn't any crap there and as I say the whole thing is intermittent.

Any thoughts/troubleshooting suggestions gratefully received

 

[picasso]

Check the temperature of the hot water going into the shower pump, the max should be around 60c but with such a big cylinder the top of the cylinder could reach 80c, do the pipes go up and over or down and then up ?

 

[mcmoby69]

With the shower set to stone cold what is the flow like?
How many litres in the 6ft cylinder and how much cold water do you have available in the tank/s above it?

 

[Madrab]

Where is the pump fed from on the HW cylinder? Give us a picture of the cylinder with the pump and associated pipework. Is the pump noisy, like it's churning air? (cavitating)

 

[mike42]

Pics attached. I've done a bit of work/investigation today. I'd be eternally grateful if I can get closer to the bottom of this!

I have the probe type thermometer and a infra-red gun style one and neither seem ideal for measuring water temp in pipes. The cylinder stat was set to 55 towards the base of the cylinder and I hadn't considered that the temperature at the top would be much higher and presumably containing/releaseing more air? So I wonder if that's the issue but how to resolve?

The other answers as best as I can are that cylidner is a Gledhill 1500x450 (so more like 5ft sorry about that). I think that makes it 210 litres. The cold tank in the loft is 50 gallons. It may be a bit too small but I've done plenty of tests with shower running for 20 minutes or more and the level gets nowhere near bottom (not even half way).

The routing you can see goes down into the pump then up out of the pump's vertical flexible hoses where an elbow routes it straight into the wall just above the skirting board. From there it goes down below the floor boards and I _think_ it just goes straight to the base of the shower head where it heads up the wall to the mixer. So I guess that is slightly down then up (with the only up/down loop formed if you include the flexible hoses of the pump if that makes any sense?)

If the the shower mixer set to stone cold the flow is very good. Today I also checked the shower when the cylinder had run out of hot water (not quite stone cold but barely warm) and the flow in the shower of hot and cold was almost identical. So this issue is definitely something to do with the temperature of the water and thanks a lot for at least hinting that that might be a factor. As a test I reduced the stat to cylinder 50 to see what happens - but that seems pretty low?

 

[AGAS]

check the filters on the pump on inlets

 

[picasso]

Wrap a bit of black tape around the pipe if you want to use an infrared thermometer.

 

[mike42]

Wrap a bit of black tape around the pipe if you want to use an infrared thermometer.

Wow - that made all the readings a lot more sensible! Anyway, with shower running with freshly heated up cylinder, I was getting a reading of 70 into the pump (I was holding the thermometer about 1cm from the pipe and taking the highest reading). That was despite the cylinder stat being set to 50 before switching on the hot water and heating the cylinder. So I'm guessing a badly placed or faulty cylinder stat at a minimum but would 70 degree water cause the flow to drop to a quarter or a third of what it should be?
So that temp of 70 is when the shower runs badly. I'll see what it is like in the morning when the tank is left alone and usually the flow is quite a bit better.

check the filters on the pump on inlets

I have done this in the past and found nothing but wouldn't that cause the issue regardless of water temperature since it would be a physical blockage? As others have kindly guided me, it looks like it only occurs when the water is actually hot.

The pump is a Techflo QT80T.

I forgot to answer the noise question and the honest answer is I don't know what it should sound like when working properly.

 

[picasso]

Water boils as 100c at atmospheric pressure, drop the pressure (in the suction side of a pump for example) and it will boil at a lot lower temp, its called cavitation and can kill the flow and shorten the life of your pump.

 

[mike42]

Ahhh - that makes a lot of sense! So you reckon that's my issue then? Bloody hell!!!! We've been pee'd off about this for years!
So what temperature should it be going into the pump? Maybe 60? Also, if it pumps ok for cold does that hopefully mean the pump itself is probably ok as long as we get the temps down?

 

[picasso]

You probably had 75c water going into the pump before you turned the cylinder stat down so may have damaged the pump, might be worth getting a blending valve fitted to the pump feed to bring the temp down to 50c or just see how it goes.

 

[mike42]

Would I have to get something (quite expensive) like http://www.plumbworld.co.uk/salamander-hot-water-supply-19181-22165
(actually not sure if that is 22mm)
Or maybe something like this would do:
http://www.screwfix.com/p/pegler-p404-tmv2-thermostatic-mixing-valve-22mm/98254

Thanks again Picasso. I can't believe we've put up with this for so long and tried so many things without realising this does seem to be the issue !

 

[picasso]

Make sure the water does not go above 60c and see how the pump copes, it might be ok with water at a reasonable temp.

 

[MeldrewsMate]

I noticed what appears to be an automatic air vent at the top of your second photo, and this would most likely be drawing in air as the pump runs. Shut it off or take it out, it has no place there!. Also make sure the hot water feed runs downward slightly on that horizontal section just out of the hot tapping, so that air will travel back to the cylinder, and vent properly. Check that the vent also runs upward all the way to the loft CWS tank, so that the air released during heating will not collect at any point.
Others have covered the effects of cavitation and hot water very well.
Have you considered heating the water in the morning too, if only to dispel the assumption that the problem is morning/evening related!

MM

 

[stevehit]

FWIW I used the Salamander valve with my Aqualisa shower pump, as our hot water cylinder has a secondary coil heated by an Aga, and the water can easily exceed the maximum permitted by the pump (60 C I seem to recall).
So, although the Salamander is expensive, you're only going to do this once...