Scalding hot water from immersion heater

[Peter Hawkins]

The immersion heater in my house is of a type I haven't seen anywhere else. There are no elements in the main tank. Instead the element is mounted inside a small vertical cylinder plumbed into the side if the tank but seperate from the main tank. Its mounted vertically with the element upside down and fitted from the bottom (which makes it hard to see the stat setting without a mirror). The secondary cylinder is 3 inches diameter and about 15 inches long.

A while back I noticed that running the immersion even for a short time produced dangerously hot water. Ther was also a bubbling noise from the cylinder when the immersion was on.

So I replaced the stat (7") set it for 60 and thought that would be that. Same problem.

Any ideas....

Peter Hawkins

[Owain]

"Peter Hawkins" wrote | The immersion heater in my house is of a type I haven't seen | anywhere else. There are no elements in the main tank. Instead | the element is mounted inside a small vertical cylinder plumbed | into the side if the tank but seperate from the main tank. | Its mounted vertically with the element upside down and fitted | from the bottom (which makes it hard to see the stat setting | without a mirror). The secondary cylinder is 3 inches diameter | and about 15 inches long.

Yes. It's called an external circulator and was often used to convert an existing cylinder with an indirect heating coil that didn't have an immersion heater boss. Because the position of the coil wasn't known, using an external circulator avoided dealing with the obstruction inside the cylinder.

It is possible the bottom connection to the cylinder is blocked which prevents water circulating. A small quantity of extremely hot water is being created at the top of the circulator and passing into the cylinder, but the cooler water from the bottom of the cyclinder is not passing into the circulator, allowing the heat to be dispersed through the whole of the cylinder. This would also mean the thermistat at the bottom never has hot water flowing over it. Bottom mounting of the heater/stat is normal.

Probably installed 1940s or 50s.

Owain

[Ed Sirett]

I've only seen one of these once before. IIRC the secondary cylinder was horizontal?

I believe that the intention is that hot HW becomes available more quickly, and/or the whole cylinder is eventually heated through. So it combines the best features of the top and bottom positioned conventional immersion heaters. It is normal for some noises to occur even with brand new immersion heaters. The replacement for this type would be an 11"(?) unit which contains a 7" thermostat (cf 27" and 11") It might be that all you need to do is to replace the thermostat (will this mean you have to cut a hole in the floor ?!?).

[Peter Hawkins]

I've already replaced the themostat. I'm sort of at a loss now, hence the posting! Could the element be at fault, causing the themostat to stay on?

Peter

[jim.]

"Peter Hawkins" TOP POSTED in message news: [e-mail]...

I've just read a very plausible explanation for this problem posted above by Owain. Are you not getting all the posts? No the stat is not cutting the element off because it's (probably) not seeing hot water, I've never seen a faulty element give the problem you describe, although technicaly I suppose it 'could' be partialy shorted out only allowing the top end to warm up. I favour the previous explanation though.

[Peter Hawkins]

Only thing is my house was built in 1995. Were these still in use then ?

[Peter Hawkins]

I'm getting all the posts, but not neccesarily in the order they're posted, suppose it depends on service providers. I was replying to Ed's post, Owains hadn't appeared at that time. The house was only built in 1995 so its less than 10 years old. Seems like a strange system for a modern house. Obviously it now seems that either the thermostat isn't being exposed to the hot water and therfore is staying shorted, or the flow is obstructed.

Just out of curiousity I put the old themostat in hot water, it trips fine...

So its not a themostat problem. Looks like I'm going to have to darin the tank whatever.

Peter

[Andrew Gabriel]

I wonder if the plumber had just removed it from someone else's house? I know of a case where that had happened (unless you can buy new hot water cylinders with so much hard water scale in them that the coil is very effectively insulated from the water).

[Pete C]

Hi,

If the thermostat is set to 60°C, the reading might not be that accurate. 60°C is 'hand hot', you should be able put your hand in for short while with only temporary discomfort! It's still way above shower temperatures, if you're concerned about kids/elderly in your house it might be worth fitting a TMV blending valve to reduce the temperature of the hot water from the cylinder.

Also is the secondary cylinder connected to the main cylinder top and bottom? If the thermostat is reading the temperature of the water from the bottom of the cylinder you might be better off connecting it via a pipe stat on the top pipe returning to the main cylinder. Also check the second cylinder is not scaled up.

cheers, Pete.

[Owain]

"Pete C" wrote | Also is the secondary cylinder connected to the main cylinder | top and bottom? If the thermostat is reading the temperature | of the water from the bottom of the cylinder you might be better | off connecting it via a pipe stat on the top pipe returning to | the main cylinder.

However the top connecting pipe will get hot very quickly, before the heater has made much difference to the bulk of the water in the cylinder.

| Also check the second cylinder is not scaled up.

I suspect scale in the lower pipe between the two.

Owain

[Owain]

"Peter Hawkins" wrote | >Probably installed 1940s or 50s. | Only thing is my house was built in 1995. Were these still in use | then | ?

I have not seen one physically, or in any contemporary literature. I think they were developed as an addition to coal-fired back boiler systems with indirect cylinders.

Owain

[Peter Hawkins]

The secondary cylinder has its bottom attachement pint about 6 incles from the main cylinder bottom. The top disappears via pipe into the wall.

I drained the tank and removed the secondary cylinder today. It was full of gunk. Flushed it out with high hopes that it might be the problem that Owain mentioned about. Howver the problem is still there. I notice that when the immersion runs the top 1/3 of the 2nd cylinder is extremley hot while the bottom 2/3 is cold. So the t'stat isn't seeing the really hot stuff. Next thing to try is a new element. Jim mentioned above that only the top may be heating, thats what it feels like.

Mind you getting the element out will be a bastard. The little secondary gives no purchase for the element spanner, and the fixing looks seized up. I imagine if I apply too much wellie the cylinder will distort !

If anyone is interested see this link for a picture

[Pete C]

secondary one and do the other two visible go to the CH?

Where do the top and middle connections visible on the cylinder go?

Does the main cylinder have another connection at the bottom out of the picture?

Is there provision for fitting an immersion heater to the main cylinder?

When the CH is run to heat DHW, which connections heat up?

Once the cylinder is heated by the CH, which pipes heat up when different hot taps around the house are used?

cheers, Pete.

[Owain]

"Peter Hawkins" wrote | The secondary cylinder has its bottom attachement pint about 6 | incles from the main cylinder bottom. The top disappears via | pipe into the wall.

Oh. Well, the hot out of the circulator needs to get back into the cylinder somehow so the water circulates.

| If anyone is interested see this link for a picture |

wonder if someone has tried to boost the output from the HW cylinder ie the heater heats the output and does not heat the tank? Does not look like the picture in Newnes c.1950

Owain

[Pete C]

secondary cylinder should connect up with the main cylinder so hot water can circulate back into it.

Do you know where the pipe at the top of the cylinder goes? My guess is that might connect to the pipe from the other cylinder elsewhere in the house, but whoever installed or modified the plumbing didn't have an appreciation for how convection works!

Is there an immersion heater boss on the main cylinder at all? If not, maybe the secondary cylinder is a way of retrofitting one where there is no provision for one, or a means of heating the whole cylinder with economy 7.

My guess is that the secondary cylinder could be connected back to the main cylinder, but making the hot connection as direct from the top of the main cylinder as possible, so that when hot water is used it is taken from the top of the main cylinder and not the bottom via the secondary one.

Also is there another pipe blanked off on the top of the main cylinder out of the picture? If so that might be the best place to connect the secondary cylinder.

cheers, Pete.

[Peter Hawkins]

One other thing to point out. I have been in this house since day 1, so this is the builders original work. The immersion is on a timer in the kitchen so I assume it heats the tank somehow.

You would think that anyway, but if that was the case, why take th etop pipe from the 2nd cylinder into the wall. Why not joint it here in the cupboard the easy way ???

There is not fitting anywhere on the tank for a standard element

The only fittings on the tank are:

2 at front for indirect coil. 1 top for drawing hot water off 1 at the bootom rear for cold feed in.

The other thing is, this all used to work OK till about 4 weeks ago...

[Owain]

"Peter Hawkins" wrote | One other thing to point out. I have been in this house since day | 1, so this is the builders original work. The immersion is on a | timer in the kitchen so I assume it heats the tank somehow. ... | The other thing is, this all used to work OK till about 4 weeks | ago...

Did you turn your CH on around that time by any chance?

I think most people are agreed that something, somewhere, has stopped the water from the circulator circulating round the cylinder. Switching on the CH or something elsewhere in the system could block the circuit or interefere with the gravity circulation (convection).

Owain

[Peter Hawkins]

Owain,

No, as its an indirect cylinder, when the CH is on we have loads of hot water. This is only ever used when the CH is not on.

I now think its the element, top half only is heating. I have the 2nd cylinder off and can see clearly down its feed pipe into the main cylinder, clear as a bell. So there is nothing to stop circulation. I can't get the element off, so I need to get a new secondary cylinder and element. I have since been told it may be called a *circulator* or

*instantaneous line heater*

Thanks

peter

[Pete C]

Hi,

Sounds like an air lock. Would be useful to know if/how the pipe from the secondary cylinder connects to the pipe at the top of the main cylinder.

cheers, Pete.