Water too Hot

slave1

Howdy all,

Background, hot water cylinder about 5 years old, immersion timer and fed from back boiler.

Issue
This last few days the water is scalding hot, unusale unless mixed with cold water its that hot
I had a problem with not hot enough/too hot during the summer and was advised to replace the thermostat which I did and all was fine up until the weekend.
Fire has been on this last week or so but don't feel this is an issue as I've never had water that hot before and have been using the back boiler for year.
Don't this water hardness can be ruining the cylinder as the water is quite good e.g. same kettle for 8 years and element virtually untouched.

Obvious thought is another dodgy thermostat but I kinda doubt that

Ideas anyone?
Tks

crosstownk

What does the thermostat control? Essentially, the thermostat cannot shut off your fire so water in the back boiler will still be heating up once the fire is lighting. Is it possible that the water was still relatively warm from the immersion heater when you lit the fire?

How is your system set up? Does the back boiler have a pump, does it heat the rads? Do you have gas or oil fired central heating too?

slave1

What does the thermostat control?
Temp of the water in tank, when it reaches the normal hot level then it switches off

Essentially, the thermostat cannot shut off your fire so water in the back boiler will still be heating up once the fire is lighting. Is it possible that the water was still relatively warm from the immersion heater when you lit the fire?
Was thinking this myself but discounted as the back boiler is not interacting in any way different than before

How is your system set up?....
Does the back boiler have a pump, does it heat the rads?
Yes, yes, again termostat control on pump and rads with termo controls too

Do you have gas or oil fired central heating too?
Oil, but not been on in months so not in the equation

crosstownk

slave1 wrote:

What does the thermostat control?
Temp of the water in tank, when it reaches the normal hot level then it switches off

In the oil fired system, when both thermostats (room and hot water cylinder) reach the set temperature then a zone valve closes, shutting off water to the respective zone. When both zones are at the desired temperature the oil fired boiler shuts down.

In your back boiler system this cannot happen - the fire stays lighting and continues to heat water in that circuit - the thermostat cannot switch off the fire.

Essentially, the thermostat cannot shut off your fire so water in the back boiler will still be heating up once the fire is lighting. Is it possible that the water was still relatively warm from the immersion heater when you lit the fire?
Was thinking this myself but discounted as the back boiler is not interacting in any way different than before.

---

If the the water in the cylinder was warm (rather than cold) then this most likely the reason. I experience this with my back boiler all the time. Sometimes I have to 'drain off' some hot water as it gets way too hot - hot enough to scald! What I do now is check to see if the water in the HWC is warm before I light the fire and if it is warm I only pull the damper out a small bit or not at all. If you are lighting the fire for a good few hours then maybe pull the damper out for an hour and then push it back for the rest of the time.


How old is the back boiler system?
How many coils are in your hot water cylinder?
Are you 100% sure the thermostat on the hot water cylinder shuts the feed to the HWC from both the back boiler as well as the OFCH?