Supply tank overflowing and radiators come with hot water on only

[Andy123]

For about a year now the radiators have been coming on with the hot water switch only on whereby i have got round this by turning the rads of but the past few weeks the small feed and overflow tank in the loft is filling up with hot water up from the airing cuboard from the feed pipe which is really hot all the way up to the tank, its not coming from the overflow pipe bent over the top of the tank but from the feed pipe at the bottom of the tank causing it to overflow onto my conservatory roof.

The system is really old about 20 years or so.

I thought it may be coil in the cylinder is broke as this would fit both symtoms but not sure.

Any thoughts appreciated.

 

[diamondgas]

I wouldn't have suspected pipework configuration as its 20 years old, although somethings off if the rads are off and it starts pumping over.

Thing is what it sounds like is happening is the exact opposite to pumping over. I call it "surging" when the pump draws negatively on the open vent and displaces the water positively up the feed. The whole system in effect is under negative pressure via the pump! Seen it quite a few times ... reason I mentioned the air is because the system volume is allowed to expand as the pump draws on the air pockets only for them to relax again under gravity when the pump shuts off! I think that makes sense..

Anyhow I'm sure we'll find out in due course should the op post up a picture....

 

[SimonG]

Thing is what it sounds like is happening is the exact opposite to pumping over. I call it "surging" when the pump draws negatively on the open vent and displaces the water positively up the feed. The whole system in effect is under negative pressure via the pump! Seen it quite a few times ... reason I mentioned the air is because the system volume is allowed to expand as the pump draws on the air pockets only for them to relax again under gravity when the pump shuts off! I think that makes sense..

Anyhow I'm sure we'll find out in due course should the op post up a picture....

Makes sense to me

 

[diamondgas]

Initial way to reduce the effect is to bleed the rads! reducing the amount of air in the system limits the quantity of system displacement ...

 

[Andy123]

Due to my last post having pics in it, it has to wait for Mod approval, however i bailed out the f/e tank again and as soon as i turned the rads on the boiler kicked in (with hot water on only) however the f/e tank did not fill up again and the feed pipe from it cooled down so it seems its not the coil after all. I checked the rads for air by the square screws at the top and no air was present.

There is a kind of electronic silver coloured boxy type valve thing after the pump connecting to T junction one going into top side of cylinder the other going downsatirs with a sliding switch at the bottom which makes no difference to the problem but we now know that with the rads on the overflow problem goes away so it must be linked to the problem of the rads coming on with the hot water only i should think.
Hope this helps for a diagnosis and many thanks for showing such an interest in my problem.

Edit: within 10 minutes of turning Rads of by the valves the f/e was filling rapidly again with the feed pipe to it getting hot almost straight away..

 

[diamondgas]

Rads coming on is a faulty diverter (silver box thing) Andy, passing to rads on ho****er only ... usually anyways

 

[diamondgas]

You need someone to check out the pipework ... What make and model boiler do you have installed?

 

[Andy123]

You need someone to check out the pipework ... What make and model boiler do you have installed?

Its a Potterton 11f
Just seen an image of a divertor on the web and thats what it looks like, i see they about £70 so it may not too expensibe a job. Will call some out.
Cheers Steve i can see why turning of the rads would make it overflow now.

 

[diamondgas]

Reason I ask about the boiler is because you could solve the issue by altering pipework or better still making your system sealed! That info doesn't compute for me though .. Is it oil or gas?

 

[diamondgas]

changing the diverter will not fix the "surging", by-the-way!

 

[Andy123]

Reason I ask about the boiler is because you could solve the issue by altering pipework or better still making your system sealed! That info doesn't compute for me though .. Is it oil or gas?

Its gas, in hindsight its worked fine for the ten years we have been in the house and the problem started with the rads coming on with the hot water and we have established that with the rads on there is no overflow issue though i accept there could be more than one problem. I could do with a quick cheap fix for a couple of years before i retire with a lump sum so i can replace the boiler and system in general.
You say the divertor wont fix the surging but will it fix rads coming on with the hot water as this would tide me over for a while at least and stop the overflow problem if its just that or am a i missing something?
Thanks for your help,
Cheers Andy.

 

[diamondgas]

New diverter will stop the radiators heating Andy ... whether that makes a difference with the hedder only time will tell eh?

 

[Andy123]

Thanks for all help guys, think i need to call someone in and will let you know the outcome.

 

[Kimou]

Thank you. It helps in the spirit of things. We are keen to know the outcome. A wise decision, sort it out before it gets worse.

"A doctor cures problems, a plumber prevents them" Queen Victoria.

 

[Andy123]

Latest update just found out by leaving the hot water of all day the f/e tank is still overlowing with a dribble, i drew a couple of pints out this morning and it was overflowing when i got home which means the core in the cylinder must be leaking too due to the higher head of water in the domestic than the f/e tank and a slight noise from the ballcock valve in there which means it must be draining.
So probably a new cylinder and a new Divertor at least.

 

[SimonG]

A bit unlucky for it not to be one or the other, looks like you've unfortunately hit the jackpot

I take it you had the cold water to the f&e tank isolated?

 

[Andy123]

A bit unlucky for it not to be one or the other, looks like you've unfortunately hit the jackpot

I take it you had the cold water to the f&e tank isolated?

Yes to be sure it was coming from the domestic header and not a leaking ballcock valve in the f/e tank.

 

[diamondgas]

Andy1123 .... To confirm that it's the cylinder coil isolate the mains cold feed to the ball valve (cap it off). That totally eliminates a passing ball valve. Next turn exerything off and wait! If the water level rises then it is definitely the cylinder...

 

[Andy123]

Yes did all the tests, Update, both the cylinder and the divertor had gone and as i have a old boiler decided to go for new Combi boiler as due to plumbing problems in the small airing cuboard it was by far the cheapest option than new system boiler with cylinder.
Best quote £1600 for a worcester 24i

 

[diamondgas]

Free & personal opinion Andy123! Get a larger boiler unless you have poor cold water supply! 24kW does not supply a great deal of hot water and can be a disapointment in the winter months. It's not the appliance more the output! Do a bit more surffing on hear and I'm sure you'll find a thread on it. Start a new thread for advice even! Take your time, you have to live with this decision not the plummer! IMHO

 

[Andy123]

Thanks for the info, i have a neighbour with the same boiler 24 kw combi so checked the flow rate which think i could live after the current situation of my daughter having a big bath and then having to wait another hour for the water to heat up but i will consider it and get quotes for a bigger one. I hear 30kW plus may require 28 mm pipes though which i have only as far as i can see the pipe from the meter up to the celiling floorboard so dont know if these continue after that or not.