Megaflo indirect cylinder thermal cut out.

[BurnageManc]

My Megaflo is producing hotter water than usual . It well may be the Thermostat has failed but I understand the Thermal cut out switch may be the cause.

Does any body know a sequence of tests/Checks that can be carried out Before changing both items.

Thanks

 

[stem]

I assume you are referring to an immersion heater. If the thermostat fails 'on' and the water overheats, the thermal cut out will trip, and switch off the heater entirely so the water would go cold after a while. The thermal cut out has to be reset manually. So, if you still continually have hot water, the cut out won't have tripped.

I imagine that it is possible for the thermostat to have become inaccurate. However, over the years I've replaced a few, and they have either failed to switch 'on' at all, or are stuck in the 'on' position.

Is there another method of controlling the temperature of the water before it's used? such as a blending valve that regulates the temperature of the water by mixing proportions of hot and cold together?

Untitled

• stem
• 23 Feb 2015
• 1

 

[BurnageManc]

I assume you are referring to an immersion heater. If the thermostat fails 'on' and the water overheats, the thermal cut out will trip, and switch off the heater entirely so the water would go cold after a while. The thermal cut out has to be reset manually. So, if you still continually have hot water, the cut out won't have tripped.

I imagine that it is possible for the thermostat to have become inaccurate. However, over the years I've replaced a few, and they have either failed to switch 'on' at all, or are stuck in the 'on' position.

Is there another method of controlling the temperature of the water before it's used? such as a blending valve that regulates the temperature of the water by mixing proportions of hot and cold together?

Untitled

• stem
• 23 Feb 2015
• 1

This is an indirect cylinder so not a stat on an immersion heater.

 

[stem]

So if I understand correctly, are you are saying you don't have an immersion heater fitted at all, and not that you have an immersion but without a thermostat

 

[BurnageManc]

So if I understand correctly you are saying you don't have an immersion heater fitted at all. If you do it will definitely have a thermostat, otherwise it would boil the water. Indirect or not.

Correct the system has a thermostat which regulates the 2 port valve which is set at 65 degrees. The water temperature is more than that so it sounds like its faulty but also there is a high limit switch (for safety) . This should turn the water off at the high limit (It may well be working as i have turned down the temp on the boiler). Is there any way of checking the thermostat and then the high limit switch.

 

[stem]

The only way I can think of that they can be tested, is to subject them to a known temperature measured with a thermometer and check to see if they operate at their prescribed settings.

This would not be easy to do in situ and probably not worth the time and effort to build a test rig in order to bench test them.

A simple test of the thermostat's basic operation, is to manually turn it up and down, does it click when you do so? Does the motorised valve open and close?

If so, you can check the operation of the motorised valve to see if it is 'letting by' when it shouldn't be, by making sure the central heating is on and running, then turn the cylinder thermostat down to its lowest setting while the water in the cylinder is hot. After a time, check that the supply pipe to the cylinder via the motorised valve has cooled. If so, the valve is closing properly.

If all is well with the valve and it is stopping flow into the cylinder, then the control of it, via the thermostat, will be the problem.

Obvious comment I know, but are you sure the thermostat hasn't been inadvertently turned up.

 

[BurnageManc]

The only way I can think of that they can be tested, is to subject them to a known temperature measured with a thermometer and check to see if they operate at their prescribed settings.

This would not be easy to do in situ and probably not worth the time and effort to build a test rig in order to bench test them.

A simple test of the thermostat's basic operation, is to manually turn it up and down, does it click when you do so? Does the motorised valve open and close?

If so, you can check the operation of the motorised valve to see if it is 'letting by' when it shouldn't be, by making sure the central heating is on and running, then turn the cylinder thermostat down to its lowest setting while the water in the cylinder is hot. After a time, check that the supply pipe to the cylinder via the motorised valve has cooled. If so, the valve is closing properly.

If all is well with the valve and it is stopping flow into the cylinder, then the control of it, via the thermostat, will be the problem.

Obvious comment I know, but are you sure the thermostat hasn't been inadvertently turned up.

Thanks for this. Your Answer reinforces what i thought but much appreciated as bouncing a thought of someone else helps.

 

[stem]

Thanks for this. Your Answer reinforces what i thought but much appreciated as bouncing a thought of someone else helps.

A bouncing of thought does indeed help. Perhaps someone else may offer another suggestion.

 

[Taylortwocities]

If I understand your set up correctly, the water is only heated by the immersion heater. Yes?

If so, the immersion should be wired in series with the thermal cut-out. This is a device that is set to disconnect the power at 90ºC. This stops the Megaflo from "boiling" if there is a fault.

The immersion heater in the megaflo has a thermostat that regulates the heat output of the immersion element. That is the set up (and there is a diagram in the Megaflo manual.

If the water is getting too hot then it will not be a problem with the thermal cut-out. It will be the thermostat that is the problem as the stat should regulate up to its maximum temperature of 70ºC. Note that the Cotherm thermostats also have their own over-temperature cut out which operates at 85ºC.

The Megaflo stat is easy to change as it just pulls out from the element body. You'll need to go to a Megaflo reseller, or on line http://www.ebay.co.uk/itm/TSE00187-...15-/191256285020?_trksid=p2141725.m3641.l6368
for example.

 

[BurnageManc]

If I understand your set up correctly, the water is only heated by the immersion heater. Yes?

If so, the immersion should be wired in series with the thermal cut-out. This is a device that is set to disconnect the power at 90ºC. This stops the Megaflo from "boiling" if there is a fault.

The immersion heater in the megaflo has a thermostat that regulates the heat output of the immersion element. That is the set up (and there is a diagram in the Megaflo manual.

If the water is getting too hot then it will not be a problem with the thermal cut-out. It will be the thermostat that is the problem as the stat should regulate up to its maximum temperature of 70ºC. Note that the Cotherm thermostats also have their own over-temperature cut out which operates at 85ºC.

The Megaflo stat is easy to change as it just pulls out from the element body. You'll need to go to a Megaflo reseller, or on line http://www.ebay.co.uk/itm/TSE00187-...15-/191256285020?_trksid=p2141725.m3641.l6368
for example.

Thanks for your reply. My system is an indirect one with the cylinder heated indirectly through the gas boiler , what you are describing is a direct cylinder installation. Thanks anyway.

 

[Taylortwocities]

OK, in that case, the Megaflo thermal cut-out goes in series with the operating circit for the DHW control valve.

Again, if you are getting hot water then its not the thermal cut out. My guess, then, would be that the water output temp control on your boiler has got wound up, or is faulty.

 

[BurnageManc]

OK, in that case, the Megaflo thermal cut-out goes in series with the operating circit for the DHW control valve.

Again, if you are getting hot water then its not the thermal cut out. My guess, then, would be that the water output temp control on your boiler has got wound up, or is faulty.

 

[BurnageManc]

OK, in that case, the Megaflo thermal cut-out goes in series with the operating circit for the DHW control valve.

Again, if you are getting hot water then its not the thermal cut out. My guess, then, would be that the water output temp control on your boiler has got wound up, or is faulty.

Its definitely not the thermal control on the boiler if I turn that down the water cools . The boiler has been set midway for years and gives us loads of water .the problem is at the Megaflo.

 

[flameport]

The thermostat may be set incorrectly. If turning it down doesn't resolve the problem, it may be defective.
Or the valve is stuck open, or some other fault is causing it to remain open.

Replacing items on unvented cylinders is not a DIY job.

 

[AlanE]

Turn the boiler off for a few hours so the pipes supplying heat from boiler to cylinder goes cold.

Now with DHW turned off fire up boiler for heating and check to see after a while if pipes to cylinder have also heated up.

If they have then the motorised valve is passing.

If they haven't heated up turn on DHW and check cylinder stat on Megaflow.