My hot water seems far too hot 🥵

[Deleted member 120897]

Greetings members of plumbersforums,

Firstly - long post alert

I’m struggling with my hot water currently - I’ve only mainly dealt with combi boilers, even then, not really had hot water too hot. Anyway I digress, my system is an open vented pre-lagged cylinder, S-plan, Myson 2 ports with a Myson cylinder stat. My hot water seems far too hot, I haven’t measured it recently, but when I did a wholeness back, I was getting 68/69 from being set at 60. I reduced it to 40, and was manageable, but still seemed hot. I’ve been been trying to “test” it today, and wife’s has said it’s gone worse. Here’s what has been done so far:

• Replaced Myson with Honeywell temporary, still same issue (although couldn’t have wired it wrong)
• 2port isn’t firing boiler by itself (that I know of)
• Checked spindle on 2 port - is fine
• Immersion heater isn’t on - checked and double checked
• Checked lever on 2 port head - not fantastic resistance
• 2 port comes on when I turn dial up on stat, and goes off when I turn it down
• Noticed just now, cylinder stat no longer clicking
• When I tested for continuity between orange and grey it brought pump on? But was my multimeter acting as a link?
• Cylinder stat is making good contact, and worked fine for approx 9 years
• Felt tank by stat, seems cold?

I have checked wiring from cylinder thermostat and is as follows:

• Common from programmer goes to terminal 1
• There’s a blue wire (assuming switch live?) in terminal 2
• Nothing in terminal 3

I read it as 3 is call for heat? I asked elsewhere and told call is terminal 2? This is where I’m struggling - can anyone explain it better? Can anyone help me test this properly? Someone has mentioned stratification?

A thanks already in advance

 

[Deleted member 120897]

Just to recap, if you turn the stat up the motorized valve opens and if you turn it down it closes.

Yes and yes, thanks.

 

[SJB060685]

So the cylinder stat reaches satisfaction and closes down the valve and shuts off the boiler?
Do you live in a hard water area by any chance?

 

[Deleted member 120897]

So the cylinder stat reaches satisfaction and closes down the valve and shuts off the boiler?
Do you live in a hard water area by any chance?

Yes, the stat is satisfied and turns off. Also 2 port was renewed by myself recently, as originally I thought it might have been the end switch sticking.

Nope, checked this recently with changing my shower valve, it’s soft I believe, comes from Lake Vrnwy in Wales.

 

[SJB060685]

Does sound like the stat shutting down is delayed. A hard water area can cause mass accumulation of limescale within and on the cylinder walls, this would cause the problem you're experiencing.
Could you upload an image of your cylinder so we can see the position of the stat?

 

[Deleted member 120897]

Does sound like the stat shutting down is delayed. A hard water area can cause mass accumulation of limescale within and on the cylinder walls, this would cause the problem you're experiencing.
Could you upload an image of your cylinder so we can see the position of the stat?

Yes no problem , I’ll do it tomorrow when the lighting is better, many thanks so far. Do you think it could still be scale even though I’m soft water area?

 

[SJB060685]

If you are definitely in a soft water area then probably not, however some areas are considered temporarily soft, meaning it can be soft some time and hard the other. I can't remember the exact figure but it's something like 150mg/litre of calcium and magnesium is considered hard and above that is considered very hard. From what you've said all electrical components are functioning as they should but it also sounds like there is a delay in the stat reading the water temperature. The only real way to see if the cylinder was fouled would be to cut it open, which I'm not advising. Does your kettle ever fur up?

 

[Deleted member 120897]

It doesn’t fur up no, just eventually scales up, which I thought happened eventually anyway as I told scale starts to come out at about 65 degrees and higher?

 

[John.g]

That would point to hard water?

 

[SJB060685]

That would indicate hard water yes and yes, at temperatures of 60°c and above the scale will start to form.

 

[John.g]

Although coil seems to be transferring heat reasonably OK, maybe remove a piece of cylinder insulation say 4/6 ins further up and see if cylinder feels (finger) hotter and attach thermostat here even if its only a temporary measure.

 

[Deleted member 120897]

As discussed, photos. Cylinder is approx 950 mm in height. Also attached is screenshots from United Utilities showing water is classed as soft.

 

[SJB060685]

The stat location looks a little low, although I couldn't say for sure where it's best placed. Perhaps @ShaunCorbs can clarify.
With the stats location and setting of 40°c the water at the top of the cylinder will naturally be hotter.
Have you got a thermometer out and actually measured the temperature of water at the taps?

 

[ShaunCorbs]

Normally 1/3 from the bottom so if it’s 36” high around 12” off the base of the cylinder

 

[SJB060685]

Normally 1/3 from the bottom so if it’s 36” high around 12” off the base of the cylinder

So looking at the image one could say the stat location isn't really ideal?

 

[John.g]

Don't know how often your top mounted immersion is used but if fairly often then these often burn out often or trip the RCD if fitted, (I have very soft water as my immersion is 49 years old) the water results certainly look soft to my untrained eye, its very strange why the cylinder feels cold adjacent to the stat, especially since its above the coil return, to absolutely rule out the stat maybe heat a pot/kettle of water to say 50/60C, hold the stat up against it and see if the dial settings correspond to its switching on/off.

 

[John.g]

So looking at the image one could say the stat location isn't really ideal?

Anywhere within the coil flow/return should be OK IMO.

 

[Deleted member 120897]

The stat location looks a little low, although I couldn't say for sure where it's best placed. Perhaps @ShaunCorbs can clarify.
With the stats location and setting of 40°c the water at the top of the cylinder will naturally be hotter.
Have you got a thermometer out and actually measured the temperature of water at the taps?

I did a while ago, and set at 50 iirc came out of the tap iirc over 60, possibly even close to 70. I need to service the boiler, so may do everything at once. Thanks.

 

[SJB060685]

You will always get layers of stratification without a destrat pump but a 20°c difference seems a lot.

 

[Deleted member 120897]

You will always get layers of stratification without a destrat pump but a 20°c difference seems a lot.

This is what I was thinking. I’ll try and move the stat up first. Thanks

 

[John.g]

You will but would expect 5 to 10C max depending on the distance between the coil flow/return, I have two coils in my cylinder, the bottom one, a solar coil has a very short distance between the flow and return and there is virtually no difference between any of the three probes, one just above the solar coil, the second about cylinder midway, the third at the cylinder top. The boiler coil which heats 100 litres of the 150 litre cylinder will gives 5/8C differential max. Would like to see the differential with a bottom mounted immersion element.

 

[SJB060685]

You will but would expect 5 to 10C max depending on the distance between the coil flow/return, I have two coils in my cylinder, the bottom one, a solar coil has a very short distance between the flow and return and there is virtually no difference between any of the three probes, one just above the solar coil, the second about cylinder midway, the third at the cylinder top. The boiler coil which heats 100 litres of the 150 litre cylinder will gives 5/8C differential max. Would like to see the differential with a bottom mounted immersion element.

I remember a post of yours a very long time ago about your cylinder and the testing you had done.
You would agree with me that a ∆T between stat and temperature at the taps of around 20°c seems a lot?

 

[Deleted member 120897]

Someone mentioned to me a few months back about checking the boiler switched live - does this sound plausible?

 

[SJB060685]

Someone mentioned to me a few months back about checking the boiler switched live - does this sound plausible?

The boiler switch live and pump live should ONLY become energised when either zone valve end switch is contacting. Using a multimeter you can prove correct operation in a couple minutes.

 

[John.g]

I remember a post of yours a very long time ago about your cylinder and the testing you had done.
You would agree with me that a ∆T between stat and temperature at the taps of around 20°c seems a lot?

Yes, couldn't see that deltaT (normally) unless the stat is faulty or dial mis positioned or cylinder motorized valve passing with boiler on CH. Other unlikely cause could be the bottom "1/2" of the coil immersed in a mountain of limescale but moving the stat up might tell alot.

 

[SJB060685]

Yes, couldn't see that deltaT (normally) unless the stat is faulty or dial mis positioned or cylinder motorized valve passing with boiler on CH. Other unlikely cause could be the bottom "1/2" of the coil immersed in a mountain of limescale but moving the stat up might tell alot.

The OP is adamant that the water in his area is soft and by the data he showed it does look very soft.