Hot water too hot

[The Doctor]

Hi, Can anyone help me please….. Ever since moving into our house a few years back the temperature of the hot water is far too hot, it’s dangerous. Now with kids it really is dangerous so I've been investigating the cause and need some advice.

I have a Telford Tornado indirect pressurised tank in an S-Plan configuration.The tank temperature is just over 80 C based on a combined pressure and temperature dial mounted on the tank (not a controlling thermostat), and what the water temperature feels like when drawing off. There is also a tank stat that controls the water temperature and this is set to 30 C

I don't believe the tank controlling thermostat is faulty, I believe it is not being exposed to the actual temperature of the tank, therefore always calling for heat (if HW ON at timer). The thermostat sensing elements are two copper tubes that go into a pocket in the side of the tank (a sort of dry immersion rather than surface mount thermostat). If I take out the sensing elements from the pocket I can get my finger a reasonable distance into the pocket but can’t feel anywhere near the heat I'd expect if it was in contact with 80 C water. Also, the copper sensing elements are not a snug fit inside the pocket therefore I question how they make enough physical contact with the pocket walls to measure temperature. Should there be a heat conducting paste or something in the pocket?

So, questions.... why should the pocket in which the controlling thermostat sits be so far below the temperature of the water inside the tank? Could lime-scale on the inside surface be creating a heat insulating layer? How 'snug' should the tank stat sensing elements be in the pocket into which they insert?

Any help gratefully received so at this point I'll hand over to you guys....

Thanks in advance.

 

[chris watkins]

Your diagnosis Doctor is pretty much spot on, all of those things could be the cause. Some dry thermostat pockets have a spring set or piece of thin metal between the two bulbs to push them against the walls to increase the conductivity however it could also be a good number of other things as well, like zone valves not working, incorrect controls or wiring etc etc.

The important thing is you need a Specialist Consultant to do the final diagnosis not a GP !!!
Under Part G of the Building Reg's it sates that only competent persons should install & maintain these un-vent hot water system because of the dangers if they not working correctly, please for the sake of your family call in an expert who has his Part G ticket to investigate the problem, if you are correct & the temp is getting that high & the stats are not working that is a real cause for concern.

BTW welcome to the forum.

PS. You can post your details on hear for a local engineer.

 

[Subby]

Another thing to consider if you have kids is to fit a blending valve (TMV) to the pipework in the bathroom, so that you can have the hot tap on the bath set to dispense water at, say 44 degrees. (like they have in the hospital)

 

[The Doctor]

Thanks for this Chris, at least I'm thinking on the right lines. I'm fairly sure its all about the thermostat, wiring conforms to the Honneywell S-plan and zone valves and other controls all functioning as I'd expect. However, I do understand that I don't know what i don't know, if you know what I mean!

So if I did call someone out and they wanted to fit a new tank stat it is a requirement to be a two stage one like that already fitted, with an over heat protection element as well as the set-point element, or would it be okay to install a single element surface mount one? I like to be an intelligent customer when these guys come in just to be on the safe side!

Stubby, I've been considering a TMV for some time. Good advice. Would still like to get the tank to a sensible temperature though.

 

[chris watkins]

These systems have to be approved i.e. tested (normally BBA) because they are a so dangerous if things go wrong they are factory fitted with the controls devices & they have to be replaced like for like!!! Now please do yourself a favour & get somebody in you knows what they are doing.

P.S. The TMV is a good idea to protect your family from scaling. If you had a new bath fitted one would have to be installed to limit the water temp to 48 deg C on the outlet. However this is not the first solution in this case as the cylinder is getting hotter than it's normal max working temperature & needs to be looked at pronto.

 

[Subby]

This is what can happen if the safety devices fail on a cylinder
exploding hot water cylinder myth busters - YouTube

 

[The Doctor]

Saw the YouTube clip, thanks Subby. Think I'll be getting someone in now.