Author Topic: Central heating pumping over  (Read 1432 times)

Aunt Maud

  • Le Flâneur.
Re: Central heating pumping over
« Reply #25 on: January 04, 2019, 04:34:17 pm »
Fingers crossed.

Re: Central heating pumping over
« Reply #26 on: January 04, 2019, 05:20:11 pm »
ah, dodgy gland then....!

cheers

Re: Central heating pumping over
« Reply #27 on: January 08, 2019, 11:16:23 am »
The saga continues. Still pumping over but possibly less amount spilling over. Yesterday, checked tightness of bleed points. Not all of them as I need a 22mm box spanner for some that have outer cases and I dont have one atm and cant find socket set  :facepalm: . Turned all rads bar upper towel rail  off initially, whacked up the room stat and ran up to boiler temp no pumping over. Boiler kettles, opens one more upper rad. No pumping over boiler quiet. Open another rad run heating no pumping over. I carried on with this running each rad up to temp and then moved on to ground floor. No pumping over. Whole operation say two hours. No pumping over bar a couple of drips. I checked the vent pipe in cyclinder cupboard each time I switched on another rad, was warm but not really that hot and cooler further up pipe. Cold feed was ok.

Heating comes on last night and yes, pumps over. What the  ???
This morning significant water on flat roof below outlet.
Could the boiler stat (thermistors Vaillant eco max pro 28)  be playing up? Digital boiler panel read out never reads more than 66 deg.
Could there still be some sludge in system?  Rads really hot though but.
By pass is working fine.Air separator was removed last year for inspection no blockage to water feed apparent. AAV on HW loop after Motorised valves currently open. I will close it again.

Pump is currently set at lower variable speed and is only 18 months old.
No wonder heating engineers run a mile when told is pumping over.
Get a bicycle. You will never regret it, if you live- Mark Twain

Re: Central heating pumping over
« Reply #28 on: January 08, 2019, 12:00:09 pm »
to me what you describe is more suggestive of something (corrosion say) producing gas in the system over time rather than the system drawing air in when it is running (unless when running normally things are somehow different than in your test; Q. is there a motorised valve in the system that might be sticking?).

Does it pump over if you stop and restart the system shortly after your (successful) test run?


A simple suggestion; it is almost certain that there is gas in the system if you fire it up after a few hours and it almost immediately pumps over, where it didn't when you restarted it before.  If you try to set light to the gas that bleeds out of radiators this may tell you if it is trapped/entrained air or gas evolved by corrosion.

However the test need not be conclusive; if the gas burns (BTW NB hydrogen flames do not look like other types of flame) it is definitely corrosion. However if it doesn't burn then there still might be corrosion.

cheers

Re: Central heating pumping over
« Reply #29 on: January 08, 2019, 01:42:21 pm »
That thought regarding a sticky motorised valve occured to me. I replaced a syncro motor to the HW water circ MV last year as it was buzzing, the other seemed ok. Moving to manual seems ok and they both close when required but as to wether they are both fully opening/closing I dunno. I could try replacing the other motor as I have a spare? Venting rads does not appear to result in any 'air' being released at all. I shall run both open on manual for a time tonight and see what happens.
Note although the replacment motors are marked as genuine 'Syncro' they are not the Honeywell versions which Honeywell state have a higher torque.
Get a bicycle. You will never regret it, if you live- Mark Twain

Re: Central heating pumping over
« Reply #30 on: January 08, 2019, 06:46:41 pm »
Two hours with both Auto valves on manual and not a drip (Well actually one drip from main tank overflow which is interesting in itself!). Cylinder stat is set to 60 Deg C so will be keeping overall temps down a bit. Boiler stat is set at 65 Deg C.  I am now about to turn over to auto.....
Get a bicycle. You will never regret it, if you live- Mark Twain

Re: Central heating pumping over
« Reply #31 on: January 08, 2019, 09:20:47 pm »
A Vaillant boiler and pouring over to me sounds like a failed expansion chamber diaphragm.  they are renowned for this failing and the cure is to fit a new boiler made by Worcester Bosch.

Been there, got the new boiler.

You may be able to fit a new external expansion chamber but basically vaillant are not good boilers.


Re: Central heating pumping over
« Reply #32 on: January 08, 2019, 09:49:58 pm »
It's a trad boiler so no expansion vessel Chris but it is a bloody mystery. IME Vaillants are pretty reliable but they have their foibles like most others. I wonder if there could be a pin hole in the cylinder coil as nothing seems to happen until max heat? Hot water is clear though but. We seem to be narrowing down to control gear and cylinder.
Get a bicycle. You will never regret it, if you live- Mark Twain

Re: Central heating pumping over
« Reply #33 on: January 08, 2019, 10:39:08 pm »
F and E overflow started dripping a few moments ago at 10:38 or so. Heating has been on all evening and appears to have stopped by 10:51.
Get a bicycle. You will never regret it, if you live- Mark Twain

Re: Central heating pumping over
« Reply #34 on: January 09, 2019, 01:51:14 am »
It's a trad boiler so no expansion vessel Chris but it is a bloody mystery. IME Vaillants are pretty reliable but they have their foibles like most others. I wonder if there could be a pin hole in the cylinder coil as nothing seems to happen until max heat? Hot water is clear though but. We seem to be narrowing down to control gear and cylinder.
Sorry, so used to sealed systems these days.

Re: Central heating pumping over
« Reply #35 on: January 09, 2019, 08:35:43 am »
River of Babylon apparent outside this morning. Sigh.........
Get a bicycle. You will never regret it, if you live- Mark Twain

Re: Central heating pumping over
« Reply #36 on: January 09, 2019, 10:03:11 am »
apologies if this is b-obvious but is it possible that your header tank is incorrectly configured?  Specifically

a) the ballcock has absolutely not to leak. Check the level in the tank (when the system is cold) and make sure that it doesn't slowly go up by itself. If in doubt shut off the cold feed to the header tank and compare.

b) there has to be an appreciable difference in the height at which the cold feed is shut off and that at which the water starts spilling into the overflow.

Even if there is no air in the system, the water expands slightly as it is heated.  The difference between the fill and overflow levels in the header tank is there to allow for such expansion. If there is a little air/gas in the system too, the expansion will be more, obviously.

When you say the system is 'pumping over' I would normally assume that this means you see water burping out of the vent pipe into the header tank. However it now seems clear that you mean that you see water coming out of the header tank overflow, which can be caused by all kinds of things, not just a fault in the heating system pipework per se. So there are some things that perhaps have not been checked yet.

It isn't at all unusual for the system to lose water by evaporation during the summer, for the ballcock to crack open, but then leak afterwards when it should be closed, eg because there is a tiny piece of limescale or something on the valve seat. The flow rate through the ballcock never gets high enough for the valve to open fully and for the limescale to be dislodged, so the leak persists.

cheers

Re: Central heating pumping over
« Reply #37 on: January 09, 2019, 11:39:16 am »
For what they cost I will swop out the ballcock and see if it has been letting by. Doubt this as I have measured water levels without heating on for several days and they have not moved. Outlet is well above normal water level.
Get a bicycle. You will never regret it, if you live- Mark Twain

Feanor

  • It's mostly downhill from here.
Re: Central heating pumping over
« Reply #38 on: January 09, 2019, 11:57:41 am »
If the Primary ( heating ) header tank is overflowing, then the water is coming from somewhere.

If the ballcock is not leaking, then the water may be entering the Primary system through a pinhole leak in the indirect coil in the hot water cylinder.
This will cause the water level in the small primary header tank to slowly equalise to the level in the larger Domestic Hot Water header tank, which will usually be higher.

Re: Central heating pumping over
« Reply #39 on: January 09, 2019, 12:21:57 pm »
If the Primary ( heating ) header tank is overflowing, then the water is coming from somewhere.

If the ballcock is not leaking, then the water may be entering the Primary system through a pinhole leak in the indirect coil in the hot water cylinder.
This will cause the water level in the small primary header tank to slowly equalise to the level in the larger Domestic Hot Water header tank, which will usually be higher.

Yep, this was the first thing our plumber said when we got an overflow from the CH header. But if it were the case it would be a continuous leak, not intermittent, no?
We are making a New World (Paul Nash, 1918)

Re: Central heating pumping over
« Reply #40 on: January 09, 2019, 03:52:11 pm »
Have replaced the ballcock with a part two float valve as they are now known and bent the arm significantly. Float is new. Water level in tank is high atm. Reducer and washer on what I thought was CW compression feed connection had me stumped for a while until I spoke to a very helpful chap at the local plumbers merchants. The old float valve certainly looked its age.

A pinhold in the coil  could be intermittent as it would not impact until the coil had heated sufficiently and then only if there were sufficent difference in head of CW tank and F and E tank. This would seem to fit the current scenario.  However,  whereas with a split coil water overlfow would run constantly. I have been told by a local heating firm that with a pin hole in the coil the hot water would be dirty and there is no obvious sign of this.
Get a bicycle. You will never regret it, if you live- Mark Twain

Kim

  • 2nd in the world
Re: Central heating pumping over
« Reply #41 on: January 09, 2019, 04:22:31 pm »
However,  I have been told by a local heating firm that with a pin hole in the coil the hot water would be dirty and there is no obvious sign of this.

Shirley that depends on which way the water's flowing through the hole.  Tip a pint of fluorescein in there and see what happens?  :D
To ride the Windcheetah, first, you must embrace the cantilever...

Re: Central heating pumping over
« Reply #42 on: January 09, 2019, 04:27:53 pm »
Pinhole in the coil will always result in tank (domestic hot) water flowing into the coil and raising the level of the (cold water primary) header, because the feed to the tank side is higher than the primary header. Why that would make the hot water dirty I've no idea.
We are making a New World (Paul Nash, 1918)

Feanor

  • It's mostly downhill from here.
Re: Central heating pumping over
« Reply #43 on: January 09, 2019, 09:49:31 pm »
I have been told by a local heating firm that with a pin hole in the coil the hot water would be dirty and there is no obvious sign of this.

As others have said, this is Just Wrong.

The standard mode of failure is as has been described.
The Domestic Hot Water ( secondary ) header tank is much larger then the small F+E tank for the Heating ( Primary ) system, and they are usually sat on the same platform.
The normal level is that the DHW tank water level is a couple of feet higher than the primary F+E tank.
Thus the hydrostatic head is usually greater in the secondary circuit.

This means that any flow through a pinhole leak is out of the DHW and into the dirty Primary system.
So no, you won't be seeing dirty Primary Loop water in the DHW.


Re: Central heating pumping over
« Reply #44 on: January 09, 2019, 09:58:32 pm »
I think it can vary with how the pumped circuit is configured and where the pressure drop is in it (in relation to any leak); the circulating pump can produce a lot more (or a lot less) pressure than 2ft of static head can.  If the header tanks are about the same height you may get a situation where the thing leaks from one circuit to another, but only when the pump is running.

cheers

Re: Central heating pumping over
« Reply #45 on: January 10, 2019, 09:58:31 am »
I think it can vary with how the pumped circuit is configured and where the pressure drop is in it (in relation to any leak); the circulating pump can produce a lot more (or a lot less) pressure than 2ft of static head can.  If the header tanks are about the same height you may get a situation where the thing leaks from one circuit to another, but only when the pump is running.

cheers

But then there would be a nett loss to the primary, so no pumping over.
We are making a New World (Paul Nash, 1918)

Re: Central heating pumping over
« Reply #46 on: January 10, 2019, 10:30:10 am »
I think it can vary with how the pumped circuit is configured and where the pressure drop is in it (in relation to any leak); the circulating pump can produce a lot more (or a lot less) pressure than 2ft of static head can.  If the header tanks are about the same height you may get a situation where the thing leaks from one circuit to another, but only when the pump is running.

cheers

But then there would be a nett loss to the primary, so no pumping over.

if the leak is in a pressurised part of the circuit, yes. But if it is the other side of a major pressure drop in the pumped circuit, the pressure could be negative vs the cylinder contents when the pump is running.  In combination with a leak that changes flowrate when it is hot or cold, and/or a sticky valve in the system there is potential for all kinds of weird behaviour.

 Best to assume little and keep an open mind about these things.   Only one thing is fairly certain; the overflow will only run if there is more gas and/or water than there should be in the pumped circuit.

One way of checking for a leak between the pumped circuit and the cylinder is to shut off the feed from the header tank into the cylinder (there is usually a valve fitted at this point, if not the hot water header tank will have to be drained), then leave a downstairs hot tap slightly open.  A bad leak will draw water from the pumped circuit and the level will go down.

 Alternatively, partially drain down the pumped circuit and pressurise the pumped circuit (to low pressure with air as described upthread).  An air  leak (i.e. above the water level in the pumped circuit) will result in a rapid pressure drop and if the leak is  in the cylinder coil t will will manifest itself as a stream of bubbles into the hot water header tank.


cheers



Re: Central heating pumping over
« Reply #47 on: January 12, 2019, 10:17:15 am »
Well....Left F and E tank at its previous high level for the last few days and guess what, no overflow at all!  :facepalm:


The float valve was the original suspect and the gaffa tape I had stuck to the side of the tank months ago to monitor the water level is still there,  though now somewhat submerged . At that time, there was no sign of the water level rising when I switched off the heating and hot water for three days, and yet it now appears that it was the ball cock all along.  Even a visit by a service engineer did not dispel my suspicion that the system was pumping over.

So a good result which has saved me considerable expense in:-

a) tracing what is actually going on
b) replacing parts that are ok ( e.g. new cylinder £600 plus)
c) not having to replace diluted inhibitor and boiler silencer.

So thanks to all for feed back and suggestions especially Brucey.

Moral of tale is should  ball cock be suspect, then change it before considering other elements. Float valves only cost a few quid and are an easy DIY replacement. (make sure you have the appropriate washer for the feed connection.)

I should of course now be thinking of changing main tank valve as well.
Get a bicycle. You will never regret it, if you live- Mark Twain