Central Heating F @ E tank feed pipe gets too hot

[dilalio]

Unless the head of the pump has been changed round, your first pic has pump direction different to your 2nd pic!

Can you confirm arrow on body of pump is pointing down?

 

[Johntheo5]

Also maybe post a photo of the pump LEDs while running, if its running on speed 3 then more than likely to cause probems as that UPS3 will pump over 18LPM at a head of 6.3M.

 

[Dereekoo]

Also maybe post a photo of the pump LEDs while running, if its running on speed 3 then more than likely to cause probems as that UPS3 will pump over 18LPM at a head of 6.3M.

What problems could this cause

 

[dilalio]

What problems could this cause

Pumping over.

 

[Harry Bloomfield]

What problems could this cause

The high head, could cause pumping over.

 

[Dereekoo]

The high head, could cause pumping over.

Not unless the cross connection between the the cold water feed and the vent/return pipe is restricted in some way i.e. full of crud, and this could also occur with a low head depending on the extent of the restriction

 

[fixitflav]

My 30L capacity F&E cistern is 300mm high so 10.0mm/litre, my system contents are around 90L so would expect the expanded vol to be ~ 1.5L so cistern level should only rise by 15mm, but assuming a 22mm cold feed of ~ 0.28L/M I presume the feed pipe should be very hot right up to the F&E cistern?, is this correct?

My figures are slightly different, but not enough to argue about!

And assuming my cistern contains ~ 15L normally, then the expanded vol of 1.5L will only raise the cistern temperature by 4/5C?.

Yes, so wouldn't expect too much of a problem. Though that's each time the system heats up, and if the F/E tank is well insulated there could be a cumulative effect.

I never seem to have noticed this on the odd time that I've felt the cold feed.

Some of the expansion occurs while the water is warming, reducing the tendency for the whole pipe to get hot.
Is this on your combined feed/vent system? Presumably that is all 22mm, and off the top of the pipe, so convection doesn't seem to be a problem there. But many boiler manufacturers (where they say anything) show cold feed via a U-bend.

Also how does the convection occur where the feed is teed in off the top of the flow pipe, does HW flow up one side of the feed pipe and cold/cooler water flow down the "other" side of the same pipe?.

Yes, and the scope for it clearly increases with pipe diameter.

 

[fixitflav]

restricted in some way i.e. full of crud,

Which seems unlikely, it all looks nice and new

 

[fixitflav]

I was forced by legislation to get a "recommended" and "gas safe" person to fit the boiler or my insurance would be invalid. This person had trouble getting the water round the system and removing trapped air so he altered my pipework to make the pump vertical and stick in this air vent (on the wrong side of the pump).

That seems a bit of a drastic solution. Systems can be slow to fill and get the air out (mine is) but surprised it couldn't be done.

but the fact remains that hot water is still migrating up the 15mm pipe and making the header tank 36 degrees. Loads of tank condensation and annoying drips out the pipe.

36° doesn't sound too bad! Which pipe is dripping, and how is it annoying?

I just find it a puzzle that the 15mm feed pipe gets very hot up to the ceiling but the overflow pipe only gets hot up about 12 inches.

Do you mean the open vent pipe? The reason is because whatever the expansion volume, most of it will go up the cold feed pipe into the F/E tank, as the area of the tank is much greater than the vent pipe.

 

[Johntheo5]

I have heard of a number of systems like the one above, mounted high up in the hot press where there was pump over especially when stopping/starting the circ pump leading eventually to air ingress, a few changed exactly to my system, no more problems, I don't know why, the dP between the vent & cold feed 125mm apart on a 22mm pipe at a flow of say 15LPM is only ~ 10mm or so.
I have the circ pump pumping into the boiler at a 3.6M head, (= actually a PP head of 4.6M), a very old rad in the upstairs (converted) attic bedroom runs with a very very slight negative head but never a problem, if you stop the circ pump, water will immediately flow from the vent screw.

 

[Johntheo5]

It would be interesting to see what @Stuck1 has the ABV set to (as well as the pump settings) because the UPS3 doesn't have any real constant curve settings, they are, in effect constant pressure, especially where you need the ABV to commence opening.

 

[dilalio]

It would be interesting to see what @Stuck1 has the ABV set to (as well as the pump settings) because the UPS3 doesn't have any real constant curve settings, they are, in effect constant pressure, especially where you need the ABV to commence opening.

Yes. Also thought about ABV - depends also if any rads are using manual valves that are left open.

 

[Stuck1]

Thanks fixitflav.
I'm interested you think 36 degrees is not to bad. I just thought it seemed a bit hot.
The pipe that is dripping is the one which leaves the top of the f&e tank and goes to the outside of the roof through the facia board. Not pouring but short periods of dripping during boiler operation. I just thought this is unusual.
Thanks johntheo5.
I originally had the ABV set at 3 but have reduced it 2. I admit that this is purely guesswork and the whole setting of these seems to me to be very hard to work out precisely.
The pump is set to 1.
Thanks Dilalio.
There are 9 TRV's. (18 rads in total all heating ok)

 

[dilalio]

Thanks fixitflav.
I'm interested you think 36 degrees is not to bad. I just thought it seemed a bit hot.
The pipe that is dripping is the one which leaves the top of the f&e tank and goes to the outside of the roof through the facia board. Not pouring but short periods of dripping during boiler operation. I just thought this is unusual.
Thanks johntheo5.
I originally had the ABV set at 3 but have reduced it 2. I admit that this is purely guesswork and the whole setting of these seems to me to be very hard to work out precisely.
The pump is set to 1.
Thanks Dilalio.
There are 9 TRV's. (18 rads in total all heating ok)

Is pump oriented with arrow on body pointing down?

 

[Johntheo5]

Thanks fixitflav.
I'm interested you think 36 degrees is not to bad. I just thought it seemed a bit hot.
The pipe that is dripping is the one which leaves the top of the f&e tank and goes to the outside of the roof through the facia board. Not pouring but short periods of dripping during boiler operation. I just thought this is unusual.
Thanks johntheo5.
I originally had the ABV set at 3 but have reduced it 2. I admit that this is purely guesswork and the whole setting of these seems to me to be very hard to work out precisely.
The pump is set to 1.
Thanks Dilalio.
There are 9 TRV's. (18 rads in total all heating ok)

The pipe that's drippng is the overflow pipe, a bit strange though if its only dripping during boiler operation, can you look into the F&E cistern when the boiler is running for awhile and check the level.
That UPS3 setting of CC1 is excellent IMO, its a max of 4.2M and probably running at ~ 3.6/3.8M at a flowrate of 16 to 18LPM.