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?

 

[quilkin]

Ah! Just found a site which says this: 'The resulting rust will end up causing a blockage, usually at the point where the cold feed enters back into the system' - so I just tested, and yes, just at that point, between the feed & expansion connections (only 2 inches!) the magnet is attracted - nowhere else!
Too late now to drain down and remove pump, but tomorrow I will do so, I should be able to dig out any blockage there, it's so close to the pump. Watch this space....

 

[Whyme]

glad you found it but we said blockage from the off.. the magnets attracted to hardened black sludge not rust. thats how magna cleans work they attract magnatite sludge and trap it. Thats also why pumps fail on sludgy systems because they create a magnetic field and it sticks and hardens...Think you should thank everybody who screamed blockage pal :smile:

 

[peteheat]

And another plumber loses a days pay........................

 

[thompsonbrown]

if your draining down to remove blockage. I would also change position of the vent & cold feed pipe work. install a air vent b4 the cylinder and replace that ball-a-fix for a gate valve.

 

[Bunker]

..and the water in the system has the inhibitor replaced at least annually

I know you said you'd put some chemical cleaner in, Id do that again then after flushing out add plenty of good quality inhibitor as whatever you have been putting in, has been failing you.

 

[diamondgas]

if your draining down to remove blockage. I would also change position of the vent & cold feed pipe work. install a air vent b4 the cylinder and replace that ball-a-fix for a gate valve.

You'd fit a valve on an expansion pipe? Scary!! Don't EVER do that quilkin!!

quilkin and Bryzer ... You'd benefit from having someone check out the pipework configuration pump speed and bi-pass settings on both your systems. Systems shouldn't pump over unless there's an issue with the layout... IMHO

 

[quilkin]

Thanks everyone for all help & suggestions. Overpumping into the header stopped now, there was rust (red rust, not black sludge) in the return pipe to the pump, just betwen the f & e pipe connections. Nowhere else, pump itself was clean; there was a bit of rust in the 3-way valve so it was sticking a bit (I cleared that before starting this thread) but not enough to block it. Also no sludge or rust visible in the manifold connections to the microbore parts.
Yes I'll put some more inhibitor in after cleaning again, I think the original problem was the expansion pipe dripping onto the tank overflow so over time the inhibitor all disappeared. Either that or my plumber didn't add any when the boiler & tank were replaced 3 years ago.

 

[Whyme]

Rust, dont see that much. Glad too hear its all sorted for ya.:yes:

 

[Bunker]

i had the same a few weeks ago, stuff was red but was built up from the rubbish at the bottom if the f&e tank.

 

[diamondgas]

i had the same a few weeks ago, stuff was red but was built up from the rubbish at the bottom if the f&e tank.

I hope you didn't leave that valve on!!!