Immersion heater bubbling into expansion tank

[zealousdp]

Firstly, I've had a good look at this and other forums for answers to the above problem...now I'd like to lay out my situation and get specific advice. Thanks in advance.

Please check my profile for pictures of the complete setup I'm discussing below, if they don't appear in this post.A

A couple days ago my mother phoned me late in the evening to say her small tank in the loft is going crazy, and was bubbling over and overflowing to the outside of the house through the overflow pipe for around half an hour.

She has a gas boiler downstairs, and an immersion water tank upstairs.

She says that if she turns the hot water on (via the control panel pictured) and doesn't turn it off after around 15mins, then the small tank "bubbles over". I noticed that the ball had split in 2, and the tank is warped - due to boiling water this time or last time several months ago. I've changed the ball, reduced the standing water in the tank to around 4 inches (it was at the overflow level before, and the ball valve arm had not been bent to only receive a few inches, bnut rather let the cold water be near the max capacity!).

I got her to turn the hot water on via control panel and indeed after about 15 mins the small tank was receiving hot water. So switched it off and haven't used it since.

The water out of the bathroom hot tap was NOT scolding or boiling...although hot enough for a shower I guess.

I THINK I understand that the small tank is supposed to receive a small amount of hot water, and the contents expand somewhat due to warmth. But, I don't understand why it happens so quickly and without fail come 15 mins of turning hot water on.

Although the immersion tank has a plug for the top (thermostat??) she doesn't plug it in.

Everything was working fine until some time back when the immersion failed for one reason or another. A certified plumber came round and decided the red pump (??) pictured needed changing...which he did and though water was restored, its never been the same. Not that it or he caused the problem, or did anything wrong, its just how my mother retells the story. Money is VERY tight for her and i'm trying to help her out using a bit of help from you and common sense and general (decent and to good standard) DIY skills.

The large tank seems unaffected. And when the heating is on this prob;em does not happen - just a small spit of water into the small tank when switching from heating to hot water on the control panel. The major incident the other night happened after having the heating on for ages (large old house needing a lot of heat!) and then leaving the hot water turned on.

The immersion is on the low pressure system (if I even needed to say that!). Am I correct in thinking that the front (honeywell) thermostat is the OLD kind and definately needs changing regardless of the above problem, so that the auto cut off works and can be reset (hope I phrased that right).

I'm on this forum as I'd like some advice before (if at all) calling out a plumber to investigate. If its a "simple" change the 1 or 2 thermostats, then a relative is an electrician and could probably safely do that once I buy the parts. Please advise what parts to change and what for if possible.

I hope I've covered everything to give a clear picture of the setup, what's happening, and my currently level of understanding.

I welcome helpful comments, please no trolling or bad-minded personal remarks about myself or mother which will be ignored and not responded to.

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[onecog]

Water feeding into the small f/e tank other than from the cold mains or vent pipe can only come from a split coil in the cylinder and would need a new cylinder.Is this what is happening ?

 

[Nige F]

the hook on the vent pipe over the small tank is too low The small tank needs replacing if it`s buckled - and more important- where will the water go if it fails - cold water makes a mess , hot water is dangerous . The overflows should be run separate , not joined together - and ideally not laying flat on the ceiling . Don`t rush into replacing things like cylinders . Some pictures of the boiler for the Gas Safe guys to comment on would be useful ( I don`t comment on boilers)

 

[Hugh Jaleak]

The small cistern (tank) is for feed and expansion, the water level will rise slightly when system is hot, and may top up via the ballvalve small amounts as and when required, but unless there's a leak it should be rarely needed. Issue sounds like it may be 'pumping over', check pump speed, if on 3 try turning down to 2, may stop it pumping over.

To the other points. The red pump has absolutely nothing to do with the immersion, but may have needed changing if both the central heating and hot water weren't working. The immersion is an alternative method to heat the tank instead of the gas boiler, advice is to use only for backup as more expensive method of heating the water. The front stat should be set at about 60deg C for the hot water, if it's set correctly but hot water is cooler than preferred it may need replacing (assuming it is wired up and operating correctly!), this controls the flow from the gas boiler to heat the cylinder, and again has nothing to do with the immersion. If working correctly it should switch the flow of hot water from the boiler to heat the cylinder off. (There is no reset on it!)

The large cistern feeds the cylinder, which in turn feeds the hot taps. The cylinder is heated by the gas boiler via a coil of copper pipe inside, thus keeping the water in the heating system and the water from the hot taps completely seperate, so rightly, the larger cistern should not be affected.

I would also strongly recommend Nige's advice is heeded.

 

[TonyW2]

First of all determine where the hot water is coming from to heat the smaller ( Heating system flow & expansion) tank.
The copper tube that is bent over the top, must be kept above the highest possible level of the water in the tank. If hot water from the c/h boiler is coming from this pipe, then try lowering the pump setting, assuggested.
Only if the tank is getting hot without any discharge from that vent pipe would there be a possibility of a hot water tank internal split.
Do follow the advice to seperate those plastic overflow pipes, but bit is not urgent or relebvant to the described problem.

 

[zealousdp]

Firstly, thank you everyone for all your comments, advice, and thoughts - I never expected such a fast and thorough response from you all.

I'll have to take time to process all that's been said and answer any questions that have been raised individually after visiting the property again Thursday/Friday.

 

[joe-90]

I welcome helpful comments, please no trolling or bad-minded personal remarks about myself or mother which will be ignored and not responded to.

It's your first post. WTF do you think you'll get comments about your mother?

 

[hazetimesfive]

yo momma

 

[JohnD]

nige is right

yes, the overflows do need to be separated.
having the two white overflow pipes connected like that could possibly lead to water from the big tank flowing into the small tank and overfilling it.

raising the bend in the vent pipe by three feet or so (try to position it so it can be clipped to a roof timber, or add a wooden support to clip it to) and having the open end well above water level (only just penetrating the lid) needs to be done. You could do this by cutting and splicing in a length of straight 22mm copper pipe to both legs with soldered (preferably) or compression joints, with no need for any pipe-bending or repositioning. If you are not fond of plumbing ask around for local recommendations.

other suggs:

Is the water level in the big tank well below the overflow level, even when no water has been used for several hours? If not, adjust the setting of the float valve in the big tank so that it won't go down the overflow. The float valve might be worn and dripping or running (easily fixed).

Also, try tying up the ball float in the both tanks for an hour, or close off the stopcock in the airing cupboard that feeds cold water to the loft, and see if the water level in the small F&E still rises when you turn the HW on at the boiler. Look in the big tank and see if the water has gone down by the same quantity that the small tank has filled which will be bad news

BTW on terminolgy:
what you are calling an "immersion" is I think the cylinder
http://www.screwfix.com/p/rm-indirect-copper-cylinder-900-x-450mm/47140

the black plastic thing on the top of the cylinder is the cap of the electric immersion heater. Yours is marked GEC which I think means it is quite old. It has its own (replacable) thermostat inside.
http://www.screwfix.com/p/27in-incoloy-immersion-heater/57798

the thermostat strapped to the front of the cylinder controls the boiler, and is quite a modern type
http://www.screwfix.com/p/honeywell-l641a-cylinder-stat/40051

the small tank in the loft is a feed and expansion tank (or cistern)

the large one is the cold water storage tank (or cistern)

BTW
Just noticed
The vent pipe over the small tank ought to be to vent the boiler.

There should be another one, coming from the top of the cylinder and going into the loft, which should be bent over the top of the large cold water tank. Is there? I can't see it in your pic. This could be very important. It is the large pipe you can see going up in the corner of the airing cupboard.

 

[davidsl500]

I had this happen to me in the eighties when the boiler stat failed and just kept heating the water in the primary until it boiled over into the expansion tank - sounded like a jet engine as it whooshed through the pipes. The DHW circuit wouldn't be very hot if the boiler has only been on 15 mins.

 

[JohnD]

my money's actually on the cylinder, but we'll see what he finds.