Replaced heat-exchanger, mixer shower hot... then not?

[woj101]

I had been having problems getting a hot shower for a while, but when the hot water around the rest of the home started failing as well I replaced the heat-exchange plate in my combi-boiler.

When I did this the shower was instantly hot again (even hotter than before because I'd been adjusting the thermostat in the mixer to try to solve the original issue) because the heat-exchanger had got all scaled up.

But it wasn't long before the shower started getting unreliable. You can turn it on, it gets fairly hot, then gets cool for a few minutes before maybe returning to warm/hot and then it may stay hot for the rest of the time its on. And then sometimes it might not get warm/hot at all.

When it does get warm, the temperature isn't really adjustable either (it used to be). I've tried adjusting the thermostat but it hasn't made any difference. The thermostat is like a small screw with some rubber over one end. You screw it anti-clockwise to make it hotter etc. but I don't really understand how it performs its function of regulating the temperature. Can this type of thermostat fail, or is it an issue in the main part of the faucet?

Thanks very much for anyone who reads, and especially to any input given.

 

[bengasman]

the new heat exchanger is probably full of sludge again, leading to the same problem

 

[tabs]

Try a new shower valve. If its a TMV then just cos the water from your boiler is coming through hotter doesn't necessarily mean your shower will be hotter. Is the water temp affected the same way at your taps?

 

[fazedup71]

try running your taps and slowing the flow rate down, does the temp suddenly go cold? as you been told it could be the shower at fault and not the boiler, but your HEX could be dirty again? your diverter valve could also be failing if the HEX was really dirty.

 

[woj101]

All other taps run hot and are not a problem.

The heat-ex was only replaced a few months ago - the previous one lasted 3 years.

Last time I had the shower unit off the wall it showed no signs of being affected by scale or sludge.

One thing I meant to add is that the HW pipe into the faucet is perfectly hot. I seems to me it's definitely an issue inside the shower - either the thermostat is haywire or it's just not mixing properly.

 

[seco services]

sounds like a cartridge issue if the pipe stays hot but shower don't.

 

[fazedup71]

Agreed!!!

 

[the.ideal.man]

isolate the cold mains to the combi boiler, then open the hot taps, if water still runs then you have crossflow. the cartridge is passing and is faulty. i for for worcester bosch as an engineer and see this quite often as most plumbers dont fit non return valves on shower mixing valves and when the cartridge goes this is what happens. if when you turn off the cold mains to the boiler the hw tap has no water then you can safely say you dont have crossflow. good luck.

 

[woj101]

My hot and cold pipes meet in the valve (i.e. there isn't a tap for each of them), so I'm unable to just turn on the hot side to see if there's crossflow.

This is my shower: http://www.showerdoc.co.uk/shower-spares/gummers/Bramham Thermostatic Valve.html

I've had the unit apart several times and can't see anything wrong with the cartridge (I'm assuming part 15 in the diagram shown in the link above is the cartridge in this instance) - can I visually inspect the cartridge for faults, or would they not be visible?

I think it's possible that I just haven't re-assembled the shower quite right, which is affecting the mix, but it's very much trial and error cos there doesn't seem to be any instructions available anywhere...