Scalding tap water from cylinder

[ross94]

Hi all, as from today we have noticed that our hot water is a lot hotter than usual, i can barely hold my hand under the tap for more than second its that hot. I have just had a shower and it was like a steam room. I have checked the tanks in the attic and nothing is boiling over the expansion pipes. We have had the central heating on more than usual today, running for several hours, could it be that the system water has become so hot it has transferred extra heat into the cylinder when the cylinder stat has called for heat? The cylinder stat has not failed as the boiler and pump are not running continuously, i have turned the stat down to 55, it was set to 60 before. What should the cylinder stat ideally be set to?
Sorry if it doesn't make much sense, could it just be that because the central heating (radiators) have been on for so long that when the hot water has called for heat the extra heat from the system has been transferred into the cylinder? The pipes that supply the coil to the cylinder are red hot, i can't put my hand on them at all.
What is going on? Does this sound normal? Like i say non of the tanks are overflowing or boiling over.
Thanks

 

[terryplumb]

Could be a number of things , cylinder stat failure ,motorised valve would be the first things to check out.

 

[CBW]

Cylinder sta may not have failed, but has it been knocked? - not touching the cylinder would also cause this problem

 

[ross94]

Cylinder sta may not have failed, but has it been knocked? - not touching the cylinder would also cause this problem

Hi, i will have a look i don't think its been knocked but i will check. What should the cylinder thermostat be set to out of interest? It was on 60 but now around 55. Is 50 okay or will that cause build up in the cylinder i forget what its called?
Thanks

 

[CBW]

60 - 65 is recommended for killing off any bacteria, such as legionella.

 

[terryplumb]

60 c would be fine

 

[ross94]

Thanks all, i will check the cylinder stat is sitting correctly and keep an eye on it, if it persists i will get British gas in. One more thing i am probably being paranoid but if the system was boiling over what are the chances of the plastic roof tank bursting? What are the general warning signs? What kind of noises would the system be making that would warn me to switch the system off? Like i say im probably being paranoid but i have a young one in the room below where the tanks are.

 

[terryplumb]

You should call in an engineer as soon as you can. The excessive tap water temperature is your warning sign.
Lower the temp of boiler. And run off a hot water tap to disperse heat in cylinder.
What boiler do you have ?

 

[ross94]

You should call in an engineer as soon as you can. The excessive tap water temperature is your warning sign.
Lower the temp of boiler. And run off a hot water tap to disperse heat in cylinder.
What boiler do you have ?

Hi, its a Worcester greenstar 18ri

 

[terryplumb]

What is the central heating temperature dial set to ,big dial on the right ? If its set to the highest setting it may be worthwhile reducing to mid or lower position .

 

[ross94]

What is the central heating temperature dial set to ,big dial on the right ? If its set to the highest setting it may be worthwhile reducing to mid or lower position .

The dial is currently set to max, i will definitely turn it down to mid, i checked the cylinder stat as well and its sitting correctly.
Thanks

 

[CBW]

The dial is currently set to max, i will definitely turn it down to mid, i checked the cylinder stat as well and its sitting correctly.
Thanks

Just an afterthought, make sure immersion heater isn’t on as well?

 

[ross94]

Just an afterthought, make sure immersion heater isn’t on as well?

Hi the immersion heater is definitely off, we haven't used that in years only once or twice when the old boiler broke down.
Thanks

 

[ianmcd]

Hi the immersion heater is definitely off, we haven't used that in years only once or twice when the old boiler broke down.
Thanks

Oh how many times have I heard that and then I turn up and guess what ? the temp of the water water produced by your gas boiler is the max temperature that the hot water in the cylinder can get to so as advised turn the boiler thermostat down and see if that solves your problem if it does you have a control fault, HW Cyl stat or zone valve fault, if it doesnt you will have to double check the Immersion heater

 

[Hugh Jaleak]

What motorised valve(s) do you have? Certain models are known to be problematic, if its stuck open to HW, then it'll keep whacking hot water from the boiler into the cylinder when the CH is calling. Possibly robbing flow from the CH, which then takes longer to get the rooms to temp, and thus exuberating the issue.