Central Heating F @ E tank feed pipe gets too hot

[Madrab]

The rise in level is due to expansion in the whole system, mainly the rads, not just the F/E tank (if it warms, which ideally it shouldn't!).

is that not what I said? It's more prevalent in larger systems as there is a greater volume to expand. If the Feed and Vent is say in an upstairs cupboard 1m below the F&E, then the warm system water will expand back up into the cistern through the feed, warming the water in the cistern.

So there are instances where an OV system's F&E cistern's water will warm up and that would be considered normal operation.

The trouble starts when the feed and vent sections start to clog up though, depending on where the actual restriction is and then the pump can start to send more water up either the feed or the vent.

 

[fixitflav]

Well, I was responding to the OP's comment that the F&E tank gets hot enough to produce "masses of condensation" which drips outside via the overflow. I don't think mere heat convection up the F&E pipe would cause this. It has to be hot water coming up the vent pipe and discharging into the F&E tank - ie overpumping.

Yes, it does seem a bit strange. perhaps he'll come back.

 

[fixitflav]

is that not what I said?

OK, see what you mean. There will be some warming of the F/E tank even without convectioin up the feed pipe. But the OP said it gets hot, not just warm. Actual temperature would be interesting.

 

[Johntheo5]

Is that a pic of your system? I thought you had a combined feed and vent.

3 things I'm not keen on
1. Pumping downwards is non-preferred.
2. The cold feed pipe should enter the circuit from underneath via a U-bend.
3. I wouldn't have open vent across the top of a tee, as it gives a head start for flow up the open vent, increasing the risk of overpumping. Better to come off a horizontal section.

Yes mine is the combined feed and vent with some rads +40 years old, inhihitor was/is only a optional extra!.

 

[Notch7]

Im surprised a new system was fitted and the OV wasnt ditched in favour of a sealed pressurised system

I thought open vented was old hat really, more prone to corrosion

 

[Madrab]

Im surprised a new system was fitted and the OV wasnt ditched in favour of a sealed pressurised system

I thought open vented was old hat really, more prone to corrosion

Some of the OV systems I look after are the cleanest systems I've seen.

Absolutely nothing wrong with an OV system, old tried and tested tech running at atmospheric pressure and very little to go wrong - does need to be looked after though and cant have leaky rads/joints. After a time the system gets conditioned with little or no O left and then it almost looks after itself.

The ones that turn into are a nightmare are the ones that aren't (edit) setup and then looked after properly.

 

[Harry Bloomfield]

Some of the OV systems I look after are the cleanest systems I've seen.

Absolutely nothing wrong with an OV system, old tried and tested tech running at atmospheric pressure and very little to go wrong - does need to be looked after though and cant have leaky rads/joints. After a time the system gets conditioned with little or no O left and then it almost looks after itself.

The ones that turn into are a nightmare are the ones that arent looked after properly.

Absolutely correct! My OV system dates from 85-ish, clean as a whistle. Now on it's third boiler, and second pump (though it didn't actually need one). Apart from which, I swapped the steel F&E tank, for a plastic one, again, not because it was leaking. It's had the water emptied out, and refilled, with inhibitor just three times.

The only real trouble, has been the 3-port valves, wearing out.

 

[fixitflav]

The only real trouble, has been the 3-port valves, wearing out.

Is it the valve or the actuator? If it's the actuator it's probably Y-plan. I've always had W-plan and no valve problems. IMO the mid-positiin function of Y-plan is of very little benefit. Sorry, pet theme of mine!

 

[fixitflav]

Yes mine is the combined feed and vent with some rads +40 years old, inhihitor was/is only a optional extra!.

One more thought on your pic - shows cold feed 22mm. Doesn't need to be, and 15mm would reduce the convection effect.

 

[Dereekoo]

I wasn't trying to say it would cause immediate problems, just that if starting from scratch I wouldn't do it that way, unless unavoidable.
Does your F/E tank get warm? The horizontal run might help reduce convection.
Can't see your pump, is it downwards?

It does get a certain amount of warmth but not to any extent to give visible issues, pump pumps downward as its situated in bathroom airing cupboard. The F/E pipe is about 1.5 m long so you may be right

 

[Harry Bloomfield]

Is it the valve or the actuator? If it's the actuator it's probably Y-plan. I've always had W-plan and no valve problems. IMO the mid-positiin function of Y-plan is of very little benefit. Sorry, pet theme of mine!

It's a Y plan, and it was regular actuator failures, but no more.... I swapped the valve and actuator a few years ago, for a MOMO type, which supported mid-position, but my latest boiler's control system doesn't make use of the mid-position. Since when, no more failures, though I still keep a spare MOMO head to hand, just in case.

I never had the water valve fail.

 

[Johntheo5]

OK, see what you mean. There will be some warming of the F/E tank even without convectioin up the feed pipe. But the OP said it gets hot, not just warm. Actual temperature would be interesting.

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?, I never seem to have noticed this on the odd time that I've felt the cold feed.
And assuming my cistern contains ~ 15L normally, then the expanded vol of 1.5L will only raise the cistern temperature by 4/5C?.

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?.

 

[Stuck1]

Thank you all for your comments so far. Much appreciated.
This is the current "H" layout on my airing cupboard.
A bit more background.....
I recently had a new Vaillant ecoplus boiler fitted. I cleaned out the system properly had all the radiators (18) off and cleaned them thoroughly. Replaced all the airing cupboard plumbing and originally had the pump horizontal and obviously no air vent!
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).
True the water gets round ok and all the rads work fine. 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.
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.

 

[Stuck1]

Just to add :-
the boiler is set at 65 degrees
there is no water entering the tank via hockeystick vent pipe when heater is on

 

[Stuck1]

This is the pipework set-up before the pump was moved.