Immersion hot water

[Ian Cowley]

We recently had the landlord and plumber round to replace our immersion heaters (plural - we're on economy 7) as both had packed up - the elements had split and shorted.

When the plumber replaced them, he put in new thermostats. Ever since, the hot water hasn't been as hot as it was before. It's most noticeable with the shower. The plumber reckons it's a venturi-style mixer, and before the work we used to have the dial about halfway round for a hot shower, now it's just hot enough when turned to the hottest setting.

This is with the immersion thermostat turned up full.

We had the plumber back, and he flushed through various pipes in case there was scale blocking the hot water pipes, all to no avail.

I've swapped the peak and off-peak thermostats (we never use peak), but it's no better. I had the landlaord round, he ran his hand under the tap and declared it fine. I brought home a digital thermocouple-type thermometer from work and the hot tap gets to a maximum of 55.8°C in the morning when the immersion heater is still on (running the tap for a few minutes).

The landlord brought round another thermostat to try, but the hot water gets to the same temperature.

The thermostat is a Heatrae Sadia 7-inch one. The instructions say it comes with the dial preset to 60°C, and it was somewhere in the middle. With it turned all the way up, we get no hotter than 56°C.

We now don't know what to do - the landlord's getting annoyed at calling out the plumber and not finidng out what's wrong, and we're getting annoyed with warm showers.

Can anyone suggest something to try? Are there different sorts of thermostats - could we get a hotter one? The ones we have audibly click in the middle of the dial range at room temperature (i.e. out of the water tank) - is that right?

[Will]

=09In my experience, the newer thermostats with the built-in=20 manually resettable over-temperature cut-outs, are made to control at a=20 much lower maximum temperature setting.

=09I suspect that it is to do with the recommendation that domestic=20 stored hot water is not maintained at a temperature higher than 65=B0C, to= =20 minimise energy wastage due to heat losses.

=09The older type thermostats used to control upto about 85=B0C, so=20 the chances are that yours was set higher than recommended. The lower=20 temperature that you are reading at the tap is likely to be partly due=20 to heat losses in the delivery pipework.

=09The thermostat should not switch in its mid-point at room=20 temperature, perhaps it had not fully cooled from its time in the tank?=20 The fact that you have two stats that operate very closely to each other=20 indicates that they are unlikely to be faulty as such, unless they both=20 came from a faulty batch...

--=20 Regards,

Will.

[watereed2003]

Seems a pretty reasonable temp to me...If the out let is reading 55 then the tank itself must be sinificantly hotter.

A comfortable shower temp is around 40 so i reckon problem is the shower itself not the tank temp per say. I know little about venturis other than what they do, but maybe the work has in some way affected the balance of hot/cold passing through...was anything else done at the same time? was all lagging replaced around hot to shower pipes? this can make a big difference on long pipe runs

ben

[Christian McArdle]

Hot water cylinders without thermostatic mixing valves should be set to between 55C and 60C. I would start looking at the shower, rather than try to increase the temperature of the cylinder dangerously.

However, with regards the adjustment, you may be setting the overheat cutout, rather than the working temperature. There should be two dials (although one or the other might be fixed temp).

Christian.

[Will]

=09I've not seen such a thermostat with an adjustable over-temp cut- out, as far as I am aware, they are all factory preset.

--=20 Regards,

Will.

[Christian McArdle]

I'm fairly sure mine is adjustable, but I might have dreamt it. It's a heat bank, so has to be set high, as the cylinder needs to run at higher temps than a standard cylinder.

Christian.

[Peter Andrews]

I recently got caught out as the thermostat needed to be turned anticlockwise to increase the temperature - I had turned it clockwise and couldn't see why the water as colder and then I got a torch and put my nose on the floor:-)

Peter

[Ian Cowley]

In message [e-mail], Will burbled:

The thermostat that was switching at room temperature was the new one from the box (which is now also giving 56°C water), so hadn't been near the tank yet. That 56°C is measured at a tap close to the tank having run the tap for a few minutes (to let the pipes heat up and everything).

I just think something's funny when I can't even get to the "factory preset" temperature of 60°C when I have the thermostat up full.

is there a chance I might need an 11" thermostat? I don't know how big the heater is, but I read somewhere that using the wrong thermostat can affect its operation...?

[Ian Cowley]

In message 42f21a2c$0$13695$ [e-mail], Christian McArdle burbled:

The cut out is a little button that pops out, apparently at 90°C according to the instructions! The thermostat is rated to operate at a "maximum continuous head temperature" of 85°C according to the instructions. i can't get it above 56!

[Ian Cowley]

In message 5KrIe.11$ [e-mail], Peter Andrews burbled:

We tried turning it the other way and it definitely got even colder. I also stuck a DVM in it to measure the resistance as I turned it :)

[Will]

=09You won't get an 11" stat into an 11" immersion heater, as the=20 pocket isn't long enough.

=09The problems occur when a 7" stat is put into an immersion heater=20 fitted vertically (or nearly vertically), as it switches the heater off=20 prematurely when the top "layer" of water reaches its set temperature.

=09Since your heater in use is the bottom one (or should be!) then a =20

7" stat is correct for the application...

--=20 Regards,

Will.

[Will]

=09This is one part that you are misunderstanding - all that this is=20 saying is that the upper operating temperature limit of the environment=20 in which the stat may be installed is 85=B0C. Not that it is designed to=20 allow the water temperature to reach this level.

=09The replacement heaters that I have installed since the new type=20 stats were introduced have all been set to the maximum temperature=20 available, a number of people have noted that the water is not hot=20 enough. Nothing that can be readily done about it...

--=20 Regards,

Will.

[Chris McBrien]

As you have access to a DVM, you could check each immersion heater itself. They should about 20 Ohms resistance if it is a 3kWatt device. MAKE SURE THE CIRCUIT IS DEAD FIRST.

If you can get to the top outlet of the immersion cylinder check the temperature there. The copper should get to water temperature quite quickly.

With both cylinders in a luke warm condition, turn the setting dial from one end to the other. You should hear a click as they open and close.

Measure the depth of the thermostat tube with a pice of stiff wire or thin wooden dowel. If the immersion is fitted in the top of the cylinder the thermostat tubes with be quite long, If they are fitted further down and across the cylinder they will be quite short 7" or so.

Chris.

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[Harry Bloomfield]

Ian Cowley expressed precisely :

With the thermostat removed, poke a piece of wire down inside the thermostat pocket. The thermostat should be close to the depth of the pocket and the element will be a little longer than the pocket.

If the element is mounted in the top of the tank, then it should be quite long in length to enable it to heat the depths of the tank. A shorter one would only heat the upper levels of the water.

[Chris McBrien]

I measured the temperature of the water comming from the bath hot tap this morning. The immersion was still on as that cuts out at 0800 hours. The temperature came to 64deg Centigrade. My bath is directly above the immersion cylinder with minimal pipework in between. I'm fairly sure that I set the thermostat to 65 - 70 deg C. as I read that 68deg C is 'Scalding' temperature.

Chris.

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[Ian Cowley]

In message [e-mail], Will burbled:

So you're saying that recent (?) changes have introduced new, lower temperature thermostats for efficiency/health and safety concerns, and that I'm unlikely ever to get my hot water above 56°C ?

If so I shall go back to the plumber and demand back the money for the time he spent aimlessly flushing non-existent scale out of the hot water pipes. Any plumber worth his salt should've known that new thermostats are cooler than old ones.

At the time I told him we didn't need new theermostats - I want the old one back!

[Will]

=09In my experience, when the "new" type 'stats came into use, the=20 maximum settable temperature was significantly reduced. I have also=20 noted that the "new" type 'stats no longer have temperatures marked=20 thereon, replaced with a "+" and "-".

=09I have perused large amounts of "official" and "non-official"=20 websites trying to find a definitive statement regarding the allowable=20 settings on the 'stats, but have only found numerous recommendations=20 that the temperature be set to "about 60=B0C"

=09It occurred to me that since your thermostat probably switches=20 your immersion off at 2.30am or thereabouts, heat losses from the tank=20 may also account for the lower temperatures you are getting at the time=20 of usage.

=09I eventually found the following site, which ought to be of some=20 help in your situation...

VKL3201, which includes the over-temp. cutout, has a max.=20 setting of 70=B0C

=09The VKL2201, which it replaces, has a max. temp. setting 10=B0C=20 higher.

=09Any contractor fitting an old type 'stat is liable to prosecution=20 in the event of an accident or incident involving it. It is possible=20 that anyone fitting one themselves may be in the same position,=20 particularly if a third party is injured...

=09See above.

--=20 Regards,

Will.

[watereed2003]

All these replies are getting confusing!

Do you think the hot at the taps (not shower) is significantly cooler than before?

If not then surely the shower is the issue? two different thermostats giving same tank temp suggests tank temp itself is not the problem.

65degrees is steaming hot! if you are getting 56 at taps then my opinion is shower/pipe run is the problem.

maybe a drop in mains pressure is preventing venturi from operating as well. was the immersion replacement the only work done?

60-65 is the recommended temp for tank, you shouldn't need it higher unless heat is being emitted over long pipe run. Lag those pipes!

[Ian Cowley]

In message [e-mail], [e-mail] burbled:

Can't really decide if the hot water temperature is lower or not - it's just bearably too hot at the moment, I think it was unbearably hot before.

The work carried out was to replace both immersion heaters and thermostats. In the process there was a lot of draining of the tank (right down) and we scopped out a lot of loose scale from the bottom of the tank (about 10 litres of scale flakes!). I think that's why the plumber thought that some scale might have been blocking the hot water pipe to the venturi shower.

No noticeable drop in mains pressure.

Hmm, it looks like the new style thermostats are giving us lower temperatures - anyone know where we can get old-style high-tem,perature thermostats?

[Pete C]

Hi,

If it's a venturi shower with mains pressure cold and a gravity fed hot try closing the stop c*ck a bit temporarily to see if reduced cold flow will give a hotter shower.

I doubt the landlord would want the HW system capable of producing scalding hot water that could injure their tenant or their freinds and relatives.

56C is about right for a maximum water temperature:

cheers, Pete.