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

 

[ShaunCorbs]

3 is hot water off eg 3 ports easy way to check set your multi meter to continuity

Probe on 1 turn the stat down 3 should beep / circuit and 2 open

Turn temp up 2 should beep / circuit 3 should be open

Where is the stat located in the tank and is touching the cylinder?

 

[Deleted member 120897]

3 is hot water off eg 3 ports easy way to check set your multi meter to continuity

Probe on 1 turn the stat down 3 should beep / circuit and 2 open

Turn temp up 2 should beep / circuit 3 should be open

Where is the stat located in the tank and is touching the cylinder?

Many thanks for the prompt reply Shaun. Yes I’ve already tested that (I’ve got a book by John Reginald - that test is mentioned, although it states it’s to find the common wire?).

Tank is approx 1m high, and stat is about 250mm from base to centre. Yes, it’s touching copper on the cylinder. After it had been on, I could place my finger in a gap and it felt cold?

 

[ShaunCorbs]

Common is live in eg terminal 1

Stat is abit low 330mm is about right 2/3 down from top

When the heating is on the port valve isn’t passing correct?

 

[Deleted member 120897]

Common is live in eg terminal 1 -thanks

Stat is abit low 330mm is about right 2/3 down from top - ok, might try moving it. It has worked ok though for number of years?

When the heating is on the port valve isn’t passing correct? Hmm?

I haven’t tried the heating, as it’s 2 port and house is like a sauna (only built 2009/2010), so no need for it too be on.

 

[Deleted member 120897]

Ordered a new Myson actuator, surely it can only be this or cylinder stat keeping it fired up? I did try a different stat which made no difference.

 

[Deleted member 120897]

Update - this hasn’t worked, although, I did probably need one, as when I removed the head again, a screw hole had snapped. Also not sure if it’s relevant, but I hear the boiler fire up, water is heated, then, say 10 mins later it’ll fire again? Could it be a thermistor?

 

[ShaunCorbs]

Does heating work ?

 

[Deleted member 120897]

It did do, I haven’t tried it yet, house is warm enough without it just now. Should I try it? If so, how long for, and do I need rads to heat up?

 

[ShaunCorbs]

A decent amount of time as that would either confirm or deny if the boilers ok

 

[Deleted member 120897]

I might have to wait until colder weather, wife and I already sweating, or do i need to do I to before then? The boiler seems to work ok, I had to replace the fan about 2 years ago due to excessive noise. The heating pump was also replaced, from a Wilo to a DAB evosta.

 

[Deleted member 120897]

Ok, just thought I’d update, had the heating on for a bit tonight, what exactly am I looking for?

 

[John.g]

Is the cylinder stat located above the heating coil return pipe?, if below it, it will "never" switch off.

 

[ShaunCorbs]

Is the pipe the flow going to the hot water the same temp as the heating aslong as you haven’t had hot water on at the same time as the heating

 

[SJB060685]

Is the cylinder stat making good contact with the cylinder? Have you done any electrical testing?

 

[Deleted member 120897]

Is the cylinder stat located above the heating coil return pipe?, if below it, it will "never" switch off.

No, it’s above it thanks.

 

[Deleted member 120897]

Is the pipe the flow going to the hot water the same temp as the heating aslong as you haven’t had hot water on at the same time as the heating

I didn’t check, didn’t know I was supposed to but I’ll do it next time.

 

[Deleted member 120897]

Is the cylinder stat making good contact with the cylinder? Have you done any electrical testing?

Thanks, I did some a while ago, cylinder stat seems to be making good contact yes, it used to work ok, but it’s now set on 40 but feels a lot hotter, haven’t measured this, but I reckon it would burn without cold mixing.

 

[SJB060685]

If the system originally worked fine then the wiring should be correct. I'd get my multimeter out and do some checks. It's going to be something simple I'm sure.

 

[Deleted member 120897]

If the system originally worked fine then the wiring should be correct. I'd get my multimeter out and do some checks. It's going to be something simple I'm sure.

I’ll be doing that again next, think it was ok though. Shaun has suggested cyl stat is too low, so need to try’s this as well. I did try a Honeywell cyl stat (which was smaller in length), and it seemed the same, so chucked it back in my van.

 

[ShaunCorbs]

Is the bulb fully home should go into the pocket around 4-8”?

 

[SJB060685]

An S plan yes? When the cylinder stat is satisfied it should close the two port and shut down the boiler. Check that that is happening.
If the stat is too low down hotter water will be at the top of the cylinder.

 

[John.g]

Thanks, I did some a while ago, cylinder stat seems to be making good contact yes, it used to work ok, but it’s now set on 40 but feels a lot hotter, haven’t measured this, but I reckon it would burn without cold mixing.

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

 

[Deleted member 120897]

Is the bulb fully home should go into the pocket around 4-8”?

Bulb and pocket? It goes into a cut hole in insulation approx depth of 1.5” touching the copper on the cylinder

 

[Deleted member 120897]

An S plan yes? When the cylinder stat is satisfied it should close the two port and shut down the boiler. Check that that is happening.
If the stat is too low down hotter water will be at the top of the cylinder.

Yes s plan, 2 port closes and shuts boiler off. Thank you

 

[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.