UK Plumber Forum

[Shafee]

Hi all,

Over the last month we noticed water coming out of all the hot taps and shower would only come lukewarm. The puzzling thing is control unit states that the temperature in the unvented cylinder is at 69-70 degrees celsius. When I’ve I released water directly from the cylinder and felt the water flowing in to the tundish it is really hot - I suspect 69-70 degrees celsius. No error codes on the boiler itself. Pressure in both expansion vessels (heating and hot water) at recommenced values. No issues with the solar panels in the loft that I can tell - its just been recently serviced.

Also a few additional notes - all radiators get to temperature fine. There is no effect to the hot water situation when the radiators are on or off. Neither is the radiator temperature affected by running the hot water.

Before we pay to have a heating engineer out does anyone have any ideas of what might be going on? The hope of course is that it is a setting that I could adjust before we pay a professional.

A massive thanks in advance!

We have the following set-up:

* Boiler - Logic Heat 15 by Ideal
* Unvented cylinder - Range Tribune HE Indirect Solar TT300 by Kingspan
* Programmable thermostats and hot water timer by Danfoss (TP9000+TP5000Si)

* Solar panels - “Clearly Solar Collectors” by Glow worm
* Solar panel system - Solar pump station and system hydraulics by Glow worm
* Fluropro solar control by Glow worm

[SimonG]

Could be a faulty shower or mixer tap back feeding cold water into the hot water.

[RPM]

Is it every hot tap in the property and any taps or showers recently changed

[Best]

Is that a blending valve I see at top of unvented cylinder?
It might be faulty if all outlets are not getting hot water despite cylinder water heated.
The blending valve could have a blockage in the hot side, but more likely the check valve has failed on the hot inlet on that valve.
That would explain the cold entering the blended hot outlet.

The cold inlet should be balanced supply ideally to that valve and hopefully is. I think looking at photo it is from balanced cold.

[Shafee]

Could be a faulty shower or mixer tap back feeding cold water into the hot water.

Possibly - will look in to that. Thank you for your reply.

[Shafee]

Is it every hot tap in the property and any taps or showers recently changed

Yes, every tap. Nothing changed out for years. Thank
You for your response.

[Shafee]

Is that a blending valve I see at top of unvented cylinder?
It might be faulty if all outlets are not getting hot water despite cylinder water heated.
The blending valve could have a blockage in the hot side, but more likely the check valve has failed on the hot inlet on that valve.
That would explain the cold entering the blended hot outlet.

The cold inlet should be balanced supply ideally to that valve and hopefully is. I think looking at photo it is from balanced cold.

Thank you for you response. It seems to be the general consensus that it is likely that the TMV has failed. At least I know where to start now. Thank you for your help.