UKC

One for any plumbers on here. Recently the lower off peak element went on our hot water tank. I replaced both off peak and the boost element as that had also gone at some point (we never use it).

I replaced both with 11inch elements and stats with thermal cut outs. This worked fine for approx 1 month then one night I hear the off peak element going through a cycle of coming on then off for approx 3 minutes all night. I opened the stat and thought it must have been faulty the contacts were charred and had possibly fused together (thermal cut out never operated). So I I then replaced this element with a 14inch as it should have been.
This has been no problem for 2 weeks then tonight it has again been constantly on and off. Could a leak on the hot water side be causing this? I.e. if there is a constant leak then the cold water supply in the cylinder will be forever pushing cold water into the tank and cooling it down causing the stat to heat the element continuously?

Or could the cold water supply isolating valve be open too much and this cold water pressure is pushing into the cylinder and causing the stat to bring the element on? Appreciate any thoughts/ideas.

In reply to dan wisey:

I would have thought that if there was hot water going somewhere you would known where it was going.  Is the hot water pipe outlet from the tank hot?  or cold?

Are the heater element's good quality i.e not far eastern crap.  I ask that as my boiler has used 2 control units in 3 years and guess where they are made.   The 1st one lasted 28 years

In reply to Removed Usercapoap: The hot water outlet is hot. The system is working well, it is just at night the element is on and off all night which it has never done before. It should just come up to temperature a few times over the night instead of on and off all night.

I can’t remember who manufactured the first 2 elements that I bought from Wickes. But the new ones I have installed are made by Tesla UK. So I doubt it could be a faulty batch of thermostats, which I have heard happening before. The system is so simple but I’m a bit flummoxed at the minute!

In reply to dan wisey:

Have you tried turning up the thermostat setting as the cycling could just indicate its set too low. You can check the temperature of the heated sections of tank using a kitchen probe thermometer to confirm the setting.

In reply to Mark Edwards:

Yeah, my wife drove me bonkers by persistantly turning the thermostat down and the boiler kept trying to keep above 60° because of Legionaires disease.

In reply to Mark Edwards:

I will tell the wife to get her screwdrivers out and give it a try as I am currently away at work. Thanks for the advice.

In reply to dan wisey:

Vented or unvented cylinder?

In reply to Chris Ebbutt:

Vented I believe as it is fed via a header tank in the loft.

In reply to dan wisey:

Is the cold cistern warm/ hot?

cylinder overheats, water lifts over into the top of the cistern, cold is drawn in at the bottom of the cylinder , repeat.

so no water is lost from the system but is being cooled in the loft and reheated in the cylinder.

this scenario is rare. More obvious, you haven’t got a dripping hot tap? 
 

assume it is a direct cylinder( no heating coil to boiler)?
 

good luck

 Chris

In reply to Chris Ebbutt: Hi Chris, yes it is a direct cylinder. No dripping taps either. 
That scenario is along the lines I was getting at in the last part of my original post.

I will check whether the cistern is warm/hot inside the loft and go from there.

Thanks for your suggestion.

In reply to dan wisey:

If the cold cistern is overflowing warm water to outside, the cycle will be even more extreme.

Are you in  a hard or soft water area.

good luck 

Chris 

In reply to Chris Ebbutt:

Soft to moderate according to the water board. To be on the safe side I fitted incoloy elements. 
It does seem a bit strange, we have never noticed any water coming out of the overflow pipe from the header tank to outside. There are definitely no leaks around the new elements either.

Thanks