Hot water too hot.

[Harry Bloomfield]

This thread is confused!

 

[Munroast]

This thread is confused!

yes, I'm not helping by butting in - will satrt my own thread later about my HW tank and its set up.

 

[BlueLoo]

yes, I'm not helping by butting in - will satrt my own thread later about my HW tank and its set up.

Take some pics

 

[dannynolan]

Thanks BlueLoo, Harry, Derekoo and CBW.

Updates:

The immersion is not on.

Photos of zone valve attached. I presume it's a three way valve.

Not sure what you mean by 'is the valve indicator showing the valve shut?' When we turn on the hot water we can hear the MPV innards moving and clicking off when we turn off the hot water. It's only a couple of years old. So presume this is working OK.

We turned the tank thermostat down to the 9 o'clock position and did not hear anything happen. When turned off to the 6 o'clock position the MPV went off so the electrics look OK.

We have now strapped the thermostat onto the cylinder so the contact should now be fine.

Any further ideas welcome.

 

[Harry Bloomfield]

Photos of zone valve attached. I presume it's a three way valve.

Not sure what you mean by 'is the valve indicator showing the valve shut?' When we turn on the hot water we can hear the MPV innards moving and clicking off when we turn off the hot water. It's only a couple of years old. So presume this is working OK.

I just cannot see if it's a 2-port or 3 in the photo, 2 port has two pipes (straight through) 3-port has three pipes like a T, but you might have a system using two 2-port valves.

Try this, turn water on as you did above, then try sweeping the thermostat setting on the cylinder from end to end. You should hear a click from the thermostat as you turn it each way and the HW valve should also run open then closed, with each alternate click.

 

[CBW]

I just cannot see if it's a 2-port or 3 in the photo.

3 Port mid position valve, 28mm too (it’s printed on the valve head).

 

[ericmark]

In the main the tank thermostat controls a motorised valve which in turn controls DHW temperature, but not always, with some C Plans the thermostat only does anything in the summer.

So if you turn off hot water at the programmer does the water go cold? If not likely the thermostat is only used in summer, if it does go cold then likely a fault.

 

[ericmark]

3 Port mid position valve, 28mm too (it’s printed on the valve head).

In which case default is DHW, it needs a supply to stop DHW not a supply to make it happen,

Grey wire is made live to stop the DHW.

 

[dannynolan]

Thanks again, will catch up with all this tomorrow.

 

[CBW]

I would try from cold, heating demand only, and then when it’s heating up, feel the pipes going to the cylinder, if they’re hot your 3 port mid position valve is stuck in the middle. It wouldn’t surprise me with the cheap valve that’s in.

 

[fixitflav]

Thanks again, will catch up with all this tomorrow.

If the cylinder stat is knackered, so calling for heat all the time (unlikely) the boiler will be on continuously while the programmer is calling for HW (burner on/off on the control-stat). If that's not happening, good chance the 3-port valve is the problem.

 

[Dereekoo]

I think either your cylinder thermostat is not working hence not telling your 3 way valve to stop sending hot water to your cylinder or your 3 way valve is not functioning correctly. Plumber or more googling to understand what is what and what you are capable of doing is required

 

[dannynolan]

Again many thanks, to everyone helping. We are just about competent enough to replace the MPV or the thermostat, will try and work out which is failing.

 

[ericmark]

I would try from cold, heating demand only, and then when it’s heating up, feel the pipes going to the cylinder, if they’re hot your 3 port mid position valve is stuck in the middle. It wouldn’t surprise me with the cheap valve that’s in.

That will not prove much, as the line will be from the programmer to make the valve travel all the way, so fault could be in the wiring.

If the cylinder stat is knackered, so calling for heat all the time (unlikely) the boiler will be on continuously while the programmer is calling for HW (burner on/off on the control-stat). If that's not happening, good chance the 3-port valve is the problem.

Two contacts the made when cold turns boiler on, the made when hot turns the water flow from valve off, so faulty made when hot can cause DHW not to turn off, but has no effect on causing boiler to turn on.

 

[DP]

Greenstar CDi Compact overview
Our Greenstar CDi Compact combi boiler is suitable for small, medium and large-sized properties with one or two bathrooms.


Are you sure?

While the OP has made a mistake, there is NO reason a combi cannot be used to heat a cylinder as well. Have done it a few times too