Water too hot

[JamesHughes]

Hi all, I've done a search on the forum and wiki, and no answer so I'll try a new topic.

My central heating/water heating appears to work fine, except the hot water is very very hot. Certainly probably 10-20degs higher than the thermostat on the HW tank is set to. In fact it doesn't appear to lower if I set the thermostat lower. I can hear it click as I move the dial, so the actual sensor part appears to be working.

The radiators can also get very hot, not so worried about that.

Heating system uses only radiator thermostatic valves - no room thermostat. Oil fired, using a working Grandee wall mounted boiler. The dial on the boiler does appear to be working correctly.

Any ideas where I should start looking for a fault, or should I expect the tank water to be hotter than the thermostat indicates?

James

 

[Terrywookfit]

Does the flow to the hot water cylinder stop when you turn the stat down?

What controls do you have ?

 

[Bamber gaspipe]

Hi all, I've done a search on the forum and wiki, and no answer so I'll try a new topic.

My central heating/water heating appears to work fine, except the hot water is very very hot. Certainly probably 10-20degs higher than the thermostat on the HW tank is set to. In fact it doesn't appear to lower if I set the thermostat lower. I can hear it click as I move the dial, so the actual sensor part appears to be working.

The radiators can also get very hot, not so worried about that.

Heating system uses only radiator thermostatic valves - no room thermostat. Oil fired, using a working Grandee wall mounted boiler. The dial on the boiler does appear to be working correctly.




Any ideas where I should start looking for a fault, or should I expect the tank water to be hotter than the thermostat indicates?

James

Change the Hot water stat.

 

[JamesHughes]

Just for added information, there is a divertor unit next to the tank. This does *appear* to work correctly, as in the summer, the rads stay cold when the heating is turned off. There is a standard programmable timer on the system, a boiler temp control and thats about it for the controls.

I have to say my first thoguhts are with the tank thermostat.

How would I check to see if the water flow to the tank goes off when stat is active? Is is just a matter of listening?

As an aside, are tank thermostats interachangeable, or do I need to replace like with like?

James

 

[JamesHughes]

And a bit more information.

I turned the heating off and checked the operation of the cylinder stat. It does appear to work correctly, in that when it clicks, the water starts to circulate. However, the water in the cylinder is about 20deg higher than what the stat is set to - so I have to increase it by 20 degs to get the pump circulating.

This makes me think that the system is heating the tank water during its room heating operation, which makes me think of the divertor, which I had thought was working OK because the rads dont heat up when only hot water is required. I think I am wrong there though, because although it may be working when the heating is off, it may not be correct when the heating is on - or its failed on some way since the summer.

So, I took the motorised unit off the divertor, and to be honest it appears that the motor side of it is working correctly. It rotates when the stat clicks to supply water to the cylinder, and afaict it returned back the heat only when the stat was turned back (Is this done under a spring or powered?). So, I checked the operation of the water valve - and this turns OK (in fact it was easily turned by hand - should it be that easy to turn? Or could there be a break meaning although the shaft is turning, the valve isnt movinh?))

So, after all that I am a bit confused - there doesnt appear to be anything wrong with anything, and yet the water is still much hotter than the stat would indicate.

The only thing I can think of, apart from the valve comment above, is that I have unjammed something during my disassembly of the diverter, and it has started working correctly. Is this likely?

James

 

[WDIK]

is your immersion heater on?

 

[JamesHughes]

Never thought to check (Have never used in since I moved in!) -but have now and it isnt.

James

 

[holty]

when you turn the cyl stat off, is the motorised valve still passing hot water to the cylinder coil

 

[JamesHughes]

Hi,

this is what I think must be happening, but how do I test whether this is the case?

James

 

[RigidRaider]

I think this might work..... can you identify the flow and return pipes to the coil in the cylinder? Try this when the system is cold, ie CH/HW haven't been on for a few hours. Turn the cylinder stat right down so it doesn't call for heat then run the heating. The flow pipe to the coil shouldn't get hot.... should it?

Theoretically also you should be able to produce the same effect by switching on only the CH at the controller, I think.

Can you borrow a thermometer and check the HW temperature? Got any neighbours who make jam? Got a lab at work?

 

[JamesHughes]

I've tried measuring the temp with an Infrared thermo, but its a bit erratic, although the temps appears to be within a deg each side of the diverter. I do need to test when the system is cold as you suggest, but that means getting up early. Still, I have an early waking 2 year old which should help.

I'm really coming to the conclusion that although the head unit of the three way divertor is working, I think the valve itself may be defective, so I may change it.

It's a Danfoss Unit, and looking in toolstation, I see that the unit itself appears to be £64.99, but buying the Programmer, cylinder stat room stat and divertor is £71.99 as a package - which seems a bit, er, odd. Esp. when all the other divertors are around £35.

Should I stick to the Danfoss, or will any old divertor do?

James

 

[holty]

i think your making this to complicated. its simple if its a three port valve, port b will be going to yor cylinder coil if its still passing hot water by touching the pipe and its hot when hot water mode is off then the valves stuck,if your hot water is reaching your taps over 60 degrees you will know as hot water at 70 degrees will scold in about a second.

 

[bengasman]

Is the cylinder stat contact surface clean, and pressed tight against the cylinder?

 

[JamesHughes]

I have now checked the valve with the HW off. System had been off overnight.

CH had been on for 20 minutes, and the HW side of the valve was actually quite hot and although difficult to tell, it did appear slightly cooler than the CH side, but still at least 50degs I would think.

Now, this could have been down to conduction as there is only about 5" of pipe work between the divertor and the tank, but to me it appears that the valve may be defective.

As I mentioned earlier, the valve itself moves very easily by hand (after taking head off) - is this expected? Or is it possible that the shaft has sheared and its not turning the valve? How difficult should it be to turn the valve by hand?

In answer to the last question, the cylinder stat is clean and firmly mounted.

James