Checking an immersion heater.

[ericmark]

I would say the first electrician should have tested the immersion heater and should have ordered up the new part and/or made safe and passed to a plumber.

I will accept that faults to thermostat, cut out, or clock may not be apparent until the element is changed.

So the following should be order of events.

One electrician visits and disconnects supply and passes job to plumber.
Two plumber changes the element.
Three electrician reconnects and changes any other faulty pats.

So you should get two bills
Plumbers bill to change element.
Electricians bill two visits one to disconnect supply and test should all be done with standard call out charge often one hour and second maybe two hours and cost of replacement parts.

If it takes three visits to work out the element has gone then you should only be charged for one visit and the company should be asking the electricians what they were playing at.

I have been in that position and have needed to call the electricians into the office and adjust the customer bill. In some cases I had to admit it was my fault for sending the wrong electrician for the job.

As foreman one can be conned and electricians can make you thing the customer is at fault. Any foreman is human and having a customer complaining can mean you go into defensive mode. So it does need some care on your part and to visit rather than phone seems to work better.

 

[westie101]

Strange

Many, many years ago the leccy board I work for always trained and expected it's electricians to be competent to change an immersion heater element without any recourse to a plumber.

Similarly they were expected to be competent to do the required plumbing for a shower

 

[peweuk]

Thanks guys.
Your views/comments seem confirm my thoughts that the element could/should have been checked/changed before/as well as just changing the thermostat.

It is also beyond me why the manager at the company stated "our guys are not trained to drain tanks" when all it needed was the mains to be turned off and the hot water taps to be opened as the tank is well above the lowest hot water output.
If he meant that they prefer their guys not to empty the tank and replace the element then he could have just said so, but again I feel this should have been mentioned early in the dialogue. My mother then would at least have had the option of looking for an alternative company who could have done the job all in one go.

@ericmark:
You stated

I will accept that faults to thermostat, cut out, or clock may not be apparent until the element is changed.

Does that mean that it is not possible or as easy to check the thermostat for a problem as it is to check the element for a fault.

The other point I picked up on visiting my mothers flat yesterday is that she has 2 immersion heaters in the tank.
When researching this issue I noted that if a tank has more than one heating element, more often than not it is recommended to change both if one needs doing. However this was not mentioned to my mother and she was not offered the option - which to me seems less that thorough.[/quote]

 

[JohnW2]

It is also beyond me why the manager at the company stated "our guys are not trained to drain tanks" when all it needed was the mains to be turned off and the hot water taps to be opened as the tank is well above the lowest hot water output.

If one wants to completely avoid 'getting wet', that's not quite enough. With a conventional vented system, the feed to hot water taps comes off the vent pipe above hot water cylinder. That means that opening hot water taps will only drain the system down to the level of that connection - hence, even if the immersion heater is mounted in the top of the cylinder, there will still be a little water above the level of the immersion, which will come out when one removes it. That can only be avoided by draining a small amount of water out of the cylinder using its drain cock (at the bottom), so that the level of water in the cylinder falls to below the level of the immersion.

Kind Regards, John

 

[Taylortwocities]

Checking the operation of an immersion heater must be one of the most simple electrical things that one can do. After all, it is simply a number of switches in series. Here's the string for the live conductor, starting at the consumer unit

MCB
Cable to immersion heater site
FCU or DP switch*
Timer (in your case)
Cable to immersion housing
Immersion thermostat
Overheat cut out
Line feed in to thermostat element

and then the neutral connection back to the consumer unit (via the switch*)

It is a simple 5 minute job to test for voltage at any point and that will narrow down the problem.

If any item is under suspicion thaen a continuity or other basic check can identify the actual problem.

Its not difficult, all that is needed is a two probe voltage tester and a logical approach. That will find 99% of problems.

Note (to the pedants) as this supposed to be a DIY forum (!) I have left out some of the more esoteric issues such as the possibility of insulation resistance issues.

And a PS. My competence is as an electrician. I hate plumbing, I do not have the tools for plumbing and every time I try to do plumbing I get wet, so I will never attempt watery stuff.
As Eric said

the first electrician should have tested the immersion heater and should have ordered up the new part and/or made safe and passed to a plumber.

 

[JohnW2]

Checking the operation of an immersion heater must be one of the most simple electrical things that one can do. After all, it is simply a number of switches in series. Here's the string for the live conductor, starting at the consumer unit
MCB
Cable to immersion heater site
FCU or DP switch*
Timer (in your case)
Cable to immersion housing
Immersion thermostat
Overheat cut out
Line feed in to thermostat element
and then the neutral connection back to the consumer unit (via the switch*)
It is a simple 5 minute job to test for voltage at any point and that will narrow down the problem.

Indeed - but the one thing one cannot easily test (without a bucket of hot water) is whether the thermostat is functional. One can verify that its contacts are closed when it is at room temperature but, without that bucket of water, one cannot determine whether they will ever open. Similarly with the 'overheat cut out', but one probably trusts that to 'operate if/when required'!

Kind Regards, John

 

[ericmark]

In the main one should highlight any faulty clock and one can show the thermostat conducts but if the thermostat allows the cylinder to go over temperature then without removing it it's had to prove.

There are today may ways of fitting a immersion heater. The Willis system uses a second tank next to main one and heats from the top of tank only the thick Irish are cleaver enough to fit these! But we also have double units with two elements at different heights and side fitting elements either wash basin and bath or off peak and on peak.

Years ago we used the water direct from the tank but today we often have hot coils or heat exchangers so hot water at mains pressure and tank vented, we also have tanks at mains pressure.

In the main the design is so opening a hot tap will never drain the tank. There are some complex systems where back boilers, solar panels, central heating and immersion heaters all heat the same tank and domestic hot water and central heating all draw on this central heat store.

So to give a 100% correct answer without seeing the system is not possible.

You say two immersion heaters the question is why? With off peak it is common to have the bottom one set to higher temperature to top one and the bottom one is feed with off peak power and top one always has power available but will not switch on until the water heated over night is used up.

However also the immersion heaters system is used to heat a small about for normal use with top one and you switch on bottom one for a bath.

Today the tanks are very well insulated using tanks like the Megaflow you have a problem knowing if hot or not feeling outside of the tank. So little heat is lost there is no point in having a clock to switch on and off as so little energy is wasted. But older tanks had little or no insulation and as a result time clocks were used to save energy.

I found my father-in-law had a fault with his hot water system in his case he had hot water solar panels and it was not until he renewed his cooker and pilot flame when out on central heating did he find there was no power to the pumps so solar panels were doing nothing. The panel fitters had used the old immersion heater supply which had two switches one by immersion heater and other in kitchen. Since he did not want to use immersion heater he switched it off in the kitchen unaware he no longer had an immersion heater and he had switched off the solar panel pumps.

I know this is not the case with you but unless you know the system it is so easy to simply switch it off without realising. He was singing the praises of solar panel water heating as his electric bill had dropped but in fact he had just swapped from electric to gas and solar panels did not do a thing.

 

[peweuk]

Thanks for the contributions guys - all makes interesting reading.

I went to mums today and drained the tank - took 20 minutes - and removed the immersion.
This is what I found

One point I would like to clarify.

As I understand it, from the comments, the thermostat has a pair of contacts (inside) which are closed when cold - allowing current flow to the element - and open when at temperature - breaking the flow.

If this is the case, on initial testing to diagnose a faulty stat, they would have had to have determined that the contacts were permanently open - what would cause the contacts to stay open?

The other thing I saw today was a note left by the electrician for mum to give the plumber. It read

Immersion Heater - Element is faulty. Requires new element with new stat + timer

however when I tested the stat the contacts were closed at room temp and opened when I heated it up with a hair dryer, which indicates correct operation - so why was he recommending it be replaced yet again.

Totally puzzling.

To satisfy my confusion I will be writing to the company to ask some very detailed questions regarding their company policy regarding fault finding procedures, as well as a detailed breakdown of the ACTUAL procedures followed by their engineers on the their visits.

Be interesting to see their response.

 

[Iggifer]

Nothing wrong with that element mate, looks mint!

 

[peweuk]

looks mint!

Hmmmmmm - that's why I can't understand why there's no hot water!!!!!!

 

[EFLImpudence]

I went to mums today and drained the tank - took 20 minutes

You were lucky. It takes hours sometimes and water comes out the screw as well.

As I understand it, from the comments, the thermostat has a pair of contacts (inside) which are closed when cold - allowing current flow to the element - and open when at temperature - breaking the flow.
If this is the case, on initial testing to diagnose a faulty stat, they would have had to have determined that the contacts were permanently open - what would cause the contacts to stay open?

Yes and nothing lasts for ever.

The other thing I saw today was a note left by the electrician for mum to give the plumber. It read

Immersion Heater - Element is faulty. Requires new element with new stat + timer

however when I tested the stat the contacts were closed at room temp and opened when I heated it up with a hair dryer, which indicates correct operation - so why was he recommending it be replaced yet again.

I suspect they always fit a new one to save an irate customer calling in a short time.
If one has been fitted recently (I haven't read all the thread again) then just being cautious, I expect.
Depends if they charged for it again.

 

[ericmark]

I would be checking the plumbing for it to fail at the top points to lack of water at some time allowing it to over heat.

the standard system is designed so you can't drain by opening the hot water tap. That means there is always water around the element.

If you can drain tank without opening a drain cock then there is something wrong.

The reason why the thermostat is changed is because of the babies death people are worried if it does go wrong or has the wrong cut out then they may be libel. If the header tank is metal or hard plastic then there are no worries only with thermal plastic can the tank burst.

Where the water heating is also done using a back boiler and a solid fuel heat source then it must have a header tank able to take boiling water and a re-settable cut out. Only where electric is only form of heating is a non re-settable cut out used the idea is should it trip then the thermostat must be faulty so it needs changing.

I lived in a house where the water boiled on a regular basis the Aga cooker simply produced too much and there was no way you didn't know it was boiling the noise was so loud. How any one could not hear there was something wrong I don't know. Maybe when the electric is the cause it's not so loud?

When it boils then also you will get pockets of steam in the cylinder which can then cause the element to over heat which would again be at the top. So if there is not a plumbing fault then likely there was a thermostat fault causing it to boil.

 

[Taylortwocities]

I do not know the layout of the immersion head. New regulations REQUIRE that there is an over-heat cutout included, to prevent boiling in the event of a fault.

A new element+thermostat should ensure that a cutout is provided. Sometimes they are in the element housing, sometimes they are part of the thermostat.

Its false economy not to replace both.

 

[peweuk]

Thanks for the comments again guys.

Just to clarify (I overlooked mentioning it in my last post) - I made an error in my statement about just opening the bath tap to drain the tank.

When I first looked at the system I could only see 2 drain cocks - one on the cold water pipe and one on the hot water pipe below the branch which fed the bath - and I just assumed, incorrectly, that this was where the tank had to be drained and the same could be effected by opening the bath tap.

On further investigation (when I went to drain the tank) I discovered a drain cock on the tank - but it was located at the bottom of the tank around the back - which made it rather awkward connecting the hose and opening/closing the valve.

In fact just as an aside I found that the positioning of most of the connections on the tank are not very convenient for where it is installed - in a small cupboard with 3 close fitting walls and one door. The only items visible, let alone easily accessible, are the immersion heaters. All the others are hidden at the back of the tank close to a wall.

 

[JohnW2]

A new element+thermostat should ensure that a cutout is provided. Sometimes they are in the element housing, sometimes they are part of the thermostat.

That's interesting. I had assumed that they were always part of the element housing, so as to be totally independent of whatever was going on in the thermostat.

Kind Regards, John