Shower cycling and cold!

[Red2k]

We have a shower over bath and the shower water is cycling hot and cold water. The shower is a concealed unit ‘Architeckt Avus PWD1283’. The water is consistently hot at the bath outlet and the bathroom tap.


We have boiler cover and so called the engineer over as this has happened previously due to build up in the heat exchanger. The boiler guy said this was a shower thermostat issue rather than boiler issue, so I replaced the thermostatic cartridge, which has not made any difference. If I keep the bathroom tap running a bit at hot temp during showers, the demand for hot water at the boiler is sufficient for the boiler (old Alpha CB28) to remain fired up and the shower then does not cycle hot/cold. Figuring that the boiler needs more hot water demand to stay fired up, I went off to try and isolate the point at which the flow might be restricted between the shower/bath diverter and the shower head. There is nothing blocking the shower hose (which is fairly new) and I even replaced the shower head with one with a 24.5 l/min flow rate.


Next stop was going to be descale/replace the shower diverter valve in case it had any build up restricting the flow. Unfortunately I’m a bit stuck on how to take this off as there does not seem to be a break between where the threading bit ends and the body begins. Considering there is a nut shape there and a retaining clip at the front end, I’m thinking its just screwed together well enough to not show the joint and one of those plumbing box spanner sets should be able to undo this?


Any other reason why the shower might be cycling? If I can get the diverter cleaned up/replaced and that does not fix it, I guess the finger points back to the boiler!


I also tried turning the hot water temp dial down to half on the boiler, in case the lower temp water reaching the thermostat meant the thermostat kept asking for hot water.

Any thoughts much appreciated!

 

[JohnD]

you've got a combi, I suppose? I think it will be flow related.

1) remove the shower head and let the water flow free from the hose or outlet at your normal comfortable temperature. Does the temperature problem go away?

If so

2) Get a bucket, fill it at the open hose or outlet; time it; calculate litres delivered per minute at your normal comfortable temperature

3) put the shower head on, fill the bucket, calculate litres per minute at your normal comfortable temperature.

4) put the shower head on, fill the bucket, calculate litres per minute with the shower at maximum hot. Does it run hot and cold?

 

[Red2k]

Thanks JohnD. Yes it is a combi.


I have tried removing the shower head and the whole hose from the wall outlet as well (which then only leaves a 6-8inch pipe run from the shower diverter to the wall outlet). The water still cycles hot and cold However, the water coming out in the bathtub is constant temp, which comes off the same supply (Boiler > shower diverter >bath or shower).

 

[JohnD]

how many litres per minute?


btw look for any of these little isolating valves, or flexible braided connection hoses

 

[Red2k]

how many litres per minute?


btw look for any of these little isolating valves, or flexible braided connection hoses

Can't spot anything like that, probably hidden behind the tiling! As I'm getting continuous hot water to the bath outlet, I am deducing that everything between the boiler and the new thermostat is working fine. Have some of the box spanners on order so I can get to the diverter valve.

 

[bernardgreen]

you've got a combi, I suppose? I think it will be flow related

Of course it is flow related........ more flow means cooler water, less flow means hotter water. That is until the boiler shuts down on over heat and the water goes cold.

It cycles hot and cold because when the boiler shuts down the water becomes cold and the over heat shut down is cancelled and the boiler fires up again

Combi huggers will say that the boiler will modulate down ( reduce heat produced ) if the water is getting too hot. A boiler can only modulate so far and at low flow rates even a fully modulated boiler will shut down because the water temperature is too high.

 

[Red2k]

So I am getting 9l per minute from the bathtub outlet and 6l per minute from the shower (with or without shower head). So looks very likely that there is a problem with the shower diverter valve.


Unfortunately I am unable to get into the diverter assembly to descale/replace it. There is a retaining clip I can get off fairly easily but there is a nut which I measure across at 22mm using an adjustable wrench. It is a bit recessed so I can’t use the adjustable wrench for this and I can’t seem to find the right size tool. I bought a socket set off amazon which goes up to 22mm, but the largest one is too small to fit. Then I found a 22mm basin wrench on screwfix, the 22mm side of which is too big! How can two things claiming to be 22mm be so widely different!? (I’m clearly missing something quite basic here!)


Any help with this goldilocks problem much appreciated!

https://www.amazon.co.uk/gp/product/B00B3T3X1A


https://www.screwfix.com/p/basin-wrench/13294

 

[bernardgreen]

Look for tube spanners

 

[Red2k]

Look for tube spanners

Thanks, I picked up a whole set of these from the amazon link above, but the 22mm has an aperture that is smaller than 22mm. So wondering if I'm missing something abvious here!

 

[Red2k]

I think I might have been a numpty while measuring the size of the backnut and what I need is a bigger tube spanner