Hot Water circulating back in to header tank via Feed

[HandOfGod]

Hi all,

I'm after some help with a vented C/H system. I've recently noticed that the expansion tank is very hot. However, the hot water is not coming in via the vent - its actually circuiting through the feed pipe. The water level is not increasing much and there is no overflow. As such I'm not expecting any problems with the cylinder.

I upgraded the pump, as I got newer, silent but higher power replacement from the in laws, 6 months ago, and realigned it to fix it against the wall. The original was hanging in free space and caused the house to shake.

Looking at the posts here pumping over is what I should be expecting - based on having too powerful a pump and there for a flow through the vent. However, given the flow is through the feed not the vent I'm coming to the conclusion that the vent is blocked forcing the hot expansion through the feed.

In the short term I've:

1. Set the pump to minimum.
2. Reduced the opening on the gate valve on the feed (to try and push more flow through the vent)
3. Reduced the thermostat settings on the boiler.

I was wondering if anyone else had the similar symptoms before I start taking the vent apart to clean them out.

Regards

Simon

 

[townfanjon]

Simon, without seeing your pump position it's hard to say , but this is what it should be ( close coupling)
Flow pipe off boiler , the first tee MUST be the vent ,second tee is the feed , these should be no more that 150mm apart and use 22mm fittings for both(reduce down for feed) then next should come your pump , again as close as possible.
Incorporate a bypass as well after pump but before zone valves.

 

[village idiot]

If it heats to the point where it has to be 'forced' back through feed pipe, try checking the cylinder stat setting as well to ensure it's not above 60•

 

[wild nomad]

Yes, all of the above! The F&E tank usually does get quite warm as heat naturally rises and it's a small tank so not much water to dissipate the heat.

How hot is the F&E tank water. Is it too hot to dip your finger in? Try using a thermometer and post the results.

Also, check that the pump is over-running for a bit after the heating and/or the hot water turns off as this is designed to dissipate the heat from the boiler.

 

[iiplumbing]

Hi HOG

I was wondering did your cold feed pipe go from the tank straight down (no bends etc) to the heating pipework.

What can also happen (and I think this is more likely than pumping over) is that the pipework is allowing vertical heat migration in the pipe. i.e. cold(ish) water comes down one side of the inside of the pipe and hot water up the other side.

more likely on 22mm than 15mm but a possibility none the less.

To prevent this you need to put in an anti gravity loop in the cold water feed pipe coming from the header tank.

Just some thoughts

Russ

 

[HandOfGod]

Thanks for the feedback all.

The Vent was blocked causing hot water to be pushed up in to the header tank via the Feed. Having put a hose pipe up it from Vent and turning it on - it flushed out some gunk.

Refilling the system after and getting it back up to temperature the system was now pumping over. This was with the pump on its lowest setting. Testing this earlier - increasing the pump speed increased the amount of pump over.

My assumption is that replacing the old 15-50 pump with the second hand (though almost new)15-60 pump caused the problem (6 month ago).

Before spending £100 on a new, less powerfull pump, I've just extended the vent an extra 30 to 40 cm above the feed tank. This seems to have stopped the pump over - but have I just caused a bigger problem?

Thanks

Simon


Some other specifics:

The feed is 15mm, the Vent is 22mm. They are teed on to a 28mm flow in to the pump in the order Boiler, Vent, Feed, Pump. The Vent and Feed are more that 150mm apart - closer to 240mm. I'm not sure this difference is critical.

The feed is a J loop in to the bottom of the tee which I understand should prevent HW circulating in the feed pipe.

 

[kay-jay]

You have stopped the pumoing over by treating a symotom and not the cause

Fitting a less powerful pump would not have been a solution either.

You have flow restriction in your circuit caused by sludge build up by the sound of things.

Add a quality branded cleanser to your system and run it for a few days when you drain it down you will get rid of a load if muck. If poss also fit a magnetic filter on the common return while system is drained [emoji3]

 

[iiplumbing]

Thanks for the feedback all.



Before spending £100 on a new, less powerfull pump, I've just extended the vent an extra 30 to 40 cm above the feed tank. This seems to have stopped the pump over - but have I just caused a bigger problem?

Thanks

Simon

Extending the vent higher up and over will do just fine. That's as good a solution as any.

from a hydraulic perspective the point at which the feed connects into the system is the system neutral point (the vent has no part in deciding what the neutral point is as it is not connected to anything). From the neutral point to the pump the pipework will be under negative pump pressure (and depending on a few factors may be under total positive or negative pressure) and everything after the pump positive pump pressure.

Pumping over occurs when the positive pump pressure exceeds the static pressure in the vent pipe at the connection to the vent pipe. (its a bit more complicated than that but that'll do for now, so extending the vent pipe mimics a higher static resistance to the pump (the water will rise but will not rise so far as to spill over). Put the vent pipe before the pump and you run the risk of sucking air into the system! This article explains it better than me

J.Mac's Pump Tool

As for sludge build up that is another issue and is caused by various factors, as Kay-jay says get a system "filter" fitted magnaclean, spiro dirt, to make sure any dirt disturbed in the system is filtered out rather than left to cause problems.

hope this helps

Russ

 

[HandOfGod]

Thanks for the guidance, I'll monitor the temperature in the expansion tank for a while and get some cleanser in the system for the week.

Simon

 

[village idiot]

If it heats to the point where it has to be 'forced' back through feed pipe, try checking the cylinder stat setting as well to ensure it's not above 60•

What an idiot!!!
pray, what has a cylinder, or its stat got to do with a Header Tank? Was suspended for TWO Weeks, and have come back more confused? I need to give up this drinking problem that I have

 

[zzzjim]

If it heats to the point where it has to be 'forced' back through feed pipe, try checking the cylinder stat setting as well to ensure it's not above 60•

And I was begining to beleive this .... Extreme hot expansion ( Only Temporary ! )

..too much pop rotting My Cells as well