Backfeexing up combined vent and cold feed

[Harvey14]

Hi all.
Just had a quick look over a commercial heating system the report was that f and e was overflowing, customer could see got water coming back up cold feed to tank they have since shut gate valve to stop it is this a case of a blockage in pipework that if have to track down.
Cheers

 

[ShaunCorbs]

Any new pump sets installed ?

 

[Harvey14]

Nah, no new pumps or changes to system problem has only just started happening.

 

[ShaunCorbs]

That's strange what's the water temp coming back into the f and e boiling ?

 

[Harvey14]

Yea I would say near to could not get hands into the tank

 

[ShaunCorbs]

Are you commercially gas safe ?

 

[Harvey14]

No not commercially gas safe just domestically and a I've had some experience with bigger systems they've asked me to have a look

 

[ShaunCorbs]

I would say get the boiler / boilers checked and make sure there not the cause if it's only just happened

Unlikely to be a blockage unless there's something really wrong with the system / works been done

Where are you located?

 

[Harvey14]

Thanks might have to pass on then,
Hot water temp seems to be ok though that tells me that any zone valves and temp controls are achieving the right temps on that side of things.
Just problem occurs when the gate valve on f and e tank is opened back up.
There are safety blowoffs on flow and returns out from the boilers which aren't letting by,
I couldn't identify where the cold feed from f and e tee's into pipework though.
I'm thinking of opening up gate valve on f and e then see if I can trace it back that way.
There shouldn't be any non return valves on the cold feed if it's a vent too?

 

[Harvey14]

North Cornwall by the way.

 

[ShaunCorbs]

Correct if combined no gate valves or nrv should be fitted

 

[Harvey14]

Thanks it may be possible as it's an old system they've taken the vent straight to outside if that is the case would mean a blocked vent? but surely the safety blowoffs would activate before it went all the way back up the cold feed.
Think it's worth another look anyways with a bit more time and try and replicate problem when I'm there.
Maybe I might get a few hints of where to start on here.
Cheers

 

[ShaunCorbs]

Not normally as boiling water and people don't mix

Maybe depends what system you have

And depends what type they are most are just pressure some pressure and temp

 

[Harvey14]

True lol.
In those cases they normally terminate them onto the roof or out the side of a building into a gulley.
Most likely to be pressure.

 

[Sparkgap]

Remember a similar problem on a school system some years ago. I believe the fault was down to pump drawing a load of water from the F&E tank and pressurising the system due to some unvented rads creating an air cushion. Tank added more water when level dropped and when the pump stopped the air pushed it back into the tank and out the overflow.
Just a thought, not knowing layout of system another common fault could be pinhole in HWS cylinder coil allowing water from HW side to enter heating if CW tank is higher.

 

[Harvey14]

Thanks in this plantroom I think the layout is the boilers and pumps just do the heating so i'l check along those lines when I go back