System overpumping into f & e tank.

[Bryzer]

Hi all, my oil fired system started over pumping late last year and found that by placing a temporary bung in the f & e feed outlet stops the overflow immediately. This is not a situation I would want to maintain and so have put up with the overpuming. This error in the system only occurs when the boiler is feeding hot water to the copper cylinder. The layout is as follows, boiler - pump- motorised valves for either requirement, from the motorised hot water valve - vent pipe - then feed into hot water coil - coil outlet - cold water feed from f & e tank - then return back to boiler. The pump is on the lowest setting, all rads are fine, have the boiler serviced annually and the water in the system has the inhibitor replaced at least annually. Gone round the usual suspect areas with the magnet for any carbon build up and all clear just like the water in the tank and the system. Any suggestions or thoughts.

 

[ne1ls0n]

overheating?

 

[Whyme]

So the vent is on the primary flow and cold feed on the primary return ( coil pipes) ?

 

[REDSAW]

port valve knacked

 

[Whyme]

Sounds like its not returning to the boiler from the cylinder. when you put the bung in its sounds like your just stopping it taking the easy route and circulating round your vent and feed..is there a gate valve on the cylinder return.? Pumping over 9 times out of ten is a blockage of some description.

 

[Bryzer]

So the vent is on the primary flow and cold feed on the primary return ( coil pipes) ?

That is correct.

 

[Bryzer]

There are no signs of overheating, in fact this situation occurs with or without radiators on flow and whatever temperature the boiler thermostat stat is set to.

 

[Bryzer]

There is a ball valve on the return back to the boiler. This replaced a gate valve about 2 years ago.

 

[Whn1]

So it pumps over from the system being cold?

 

[Bryzer]

So it pumps over from the system being cold?

Yes as soon as the water has heated up in the coil.

 

[tamz]

Gravity conversion to fully pumped done by a halfwit.

 

[alexmurchison]

shouldnt the f + e be before the pump !!

 

[quilkin]

I have a very similar problem. water is being drawn into the system through the feed from the tank, and simulatneously hot water is flowing out of the expansion pipe - but only when the 3-way-valve is in water only or water+heat positions. With just heat it's OK. The feed pipe is fitted about 4" from the pump inlet; the expansion pipe about 8" from the inlet; no other connections in these 8 inches. There is a cut-off valve in the feed pipe and as soon as this is closed the overflow through the expansion pipe stops, so it's not the overflow causing the problem. All temperatures are fine.
For ages I have been playing with the 3-way valve, assuming that's the problem but it appears to be working fine, anyway most of my experiments have been with the 3-way valve motor removed and me adjusting the position by hand.
I have recently run the system for 4 days with cleaner , assuming a blockage but all clean now and still the same problem. And if it was a blockage, I don't understand why it works OK with only heating - where is there is mostly microbore - the hot water circuit is very short (same cupboard as pump & valve) and is all 22mm pipes.
Any ideas?

 

[Howsie]

Call a plumber

 

[Whyme]

welcome quilkin. if there isnt a blockage or restriction (valve etc) it wouldnt be forced up and over the tank. Unless its over heating, you say its niether so dunno im afraid.

 

[quilkin]

If it was a blockage, I would expect the water to be forced up the expansion pipe regardless of the state of the feed pipe being closed or not. But the overflow stops immediately I shut off the feed valve. It seems there is some sort of venturi effect actually pulling water into the system via the feed pipe.

 

[alexmurchison]

is the vent pipe correctly positioned over the tank ie high enough ?

 

[quilkin]

Yes. In fact I only started to notice the problem originally because the vent pipe was originally slightly overhanging the overflow from the tank, and a few drops were running out of the overflow and outside. (I've moved the vent pipe since!)

 

[Whyme]

Usually when the 'feed' pipe is closed youve stopped it circulating around the vent back into the tank ,up the vent and back into the tank and on and on, which from my experiance usually means a circulation problem. On return etc. if its pumping over and no pipework alterations are the cause its blocked or 'restricted' or it would take the easiest route through the coil and back to the boiler. somebody else will be along soon no doubt to throw a few more ideas around.

 

[alexmurchison]

i agree. if all visual pipework is layed out correctly....position of overflow / pump / valves etc, then there must be some restriction , especially if you say its fine when on heating only, and pumps over when on both or water, when on water only does the pipework beyond the zone / diverter valve get hot. does the full length of pipework back to the boiler get hot? is there an inline filter that could be blocked / restricted. Does the system have a bypass ?

 

[Ryan Jones]

From what you've described I'd say the piping layout is wrong. You say that the vent is after the HW motorized valve. So where does your system vent when you have heating only? I'd call a plumber quick whilst this is the least of your problems!

 

[Bunker]

Mods to move to Central Heating forum?

 

[quilkin]

Oops, I wasn't aware there was a separate forum, sorry. Probably better there if it can be moved.
Ryan, the vent (and the feed as well) are immediately before the pump, i.e after all the returns have joined via the boiler.
Alexmurchison, I turned everything off for 2 hours and then turned on hot water only. Pipes to & from hot tank, and return pipe through pump, all get hot quickly, as expected. Doesn't appear to be any blockage there. No filter or bypass, although there is a rad in the bathroom (next to hot tank)which is on the hot water circuit - but that heats up OK.
I just can't understand, if it's a blockage, why it would still be a problem with both heating & water activated, but not with just heating activated. Which section could the blockage be in? If the problem occured only with 'just hot water', or only with 'just heating', it would be obviously a blockage in the relevant section.

 

[alexmurchison]

hmmm, baffles me, just a thought but is the pump, "pumping" in the right direction ? not towards the feed and vent !

 

[Bryzer]

Any suggestions, or will the pipework have to be re-routed in order to overcome this issue?