Deteriorating hot water temperature from one (mixer) tap - no clear solution!?

[potato80]

Hi all. Any obvious reason why this mixer tap is delivering increasingly cooler water? Was never very hot to begin with, but is now delivering only lukewarm/cold water. Flow seems ok.

Boiler, CH and all other taps above and below this one are all working fine.

Any advice much appreciated

 

[Johntheo5]

What happens if you shut off the cold water isolating gate valve?.

 

[potato80]

If I turn the hot tap on and then turn the valve highlighted in yellow off, then a very slow tiny trickle of water continues to come out.

The other valve (highlighted in blue) is too difficult to turn.

Am actually starting to wonder if I've basically got two hot water systems in the house, with this bath being fed from the hot water tank, and all the other taps being fed from the boiler. Tank seems thoroughly hot.

 

[Deleted member 267285]

If I turn the hot tap on and then turn the valve highlighted in yellow off, then a very slow tiny trickle of water continues to come out.

The other valve (highlighted in blue) is too difficult to turn.

Is the highlighted yellow one the hot?

 

[Johntheo5]

Does the water eventually get hot or does the copper pipe underneath the (yellow) isol valve get hot?. If you remove the handwheel from the blue isolating valve you should be able to turn it with a adjustable spanner, if you free it up shut both isol valves, remove both upstream pipes and open the valves a bit to see if you get a good flow of water from both, if so, probably the thermostatic cartridge?

 

[terryplumb]

Is your hot water from a combi boiler ?
The valve in blue is the cold feed. Yellow is the hot.

 

[potato80]

Is the highlighted yellow one the hot?

Not sure, but I think so (cos of the connected wires)

 

[potato80]

Is your hot water from a combi boiler ?
The valve in blue is the cold feed. Yellow is the hot.

Good question. I just edited my original post. I think I might have two systems, with this bath - potentially - fed from a tank. boiler might be doing all the other outlets, hence them being ok. Tank seems hot though, so might be another issue

 

[terryplumb]

Are you sure your boiler is a combi ,would be unusual to have a hot water cylinder as well ?

 

[potato80]

Are you sure your boiler is a combi ,would be unusual to have a hot water cylinder as well ?

Ecotec plus 630

 

[potato80]

Does the water eventually get hot or does the copper pipe underneath the (yellow) isol valve get hot?. If you remove the handwheel from the blue isolating valve you should be able to turn it with a adjustable spanner, if you free it up shut both isol valves, remove both upstream pipes and open the valves a bit to see if you get a good flow of water from both, if so, probably the thermostatic cartridge?

I'll try and check this now. Thank you!

 

[terryplumb]

That's a system boiler ,not a combi. What type of cylinder do you have ?

 

[potato80]

That's a system boiler ,not a combi. What type of cylinder do you have ?

An old one!

 

[terryplumb]

Thanks ,that's an unvented cylinder and delivers hot water under mains water pressure.
If you isolate the mains cold water where it enters the building ,drain hot and cold taps ,then remove your bath mixer ,and check the inlet filter on the hot inlet of the mixer valve. If it's clean ,your showers thermostatic valve is faulty and needs replacing.