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patrick · Joined: 13 Feb 2003 Posts: 7

I have an oil-fired system providing hot water and central heating through a microbore system basic on a 3-port valve. All works well except for a regular drip from the overflow of the header tank. The ball-cock is working OK. I've bent the ball-cock to reduce the volume in the header tank and still it overfills.

What is happening to cause the overflow? The expansion tank is a regular size and is set to be ablout 1/2 full.

Thanks

Ian · Moderator Joined: 18 Feb 2003 Posts: 32 Location: wigan

patrick · Joined: 13 Feb 2003 Posts: 7

Thanks for the reply - daft question - your suggestion about the coil having a pin hole - the expansion tank and cold water feed tanks are both in the loft and the hot water cylinder is in the room below. Is that what you are describing? Is there any way that I can determine that this is the problem?

Re. overheating - there is a trip on the boiler - if that isn't tripping, does it mean that the stat is OK? It doesn't run continually and is set to about 60degC.

The pump is on the second of three settings pushing through a microbore system with 7 rads - all but 2 have TRVs - the other two are heat dumps for the boiler. I guess your idea about the pump setting could be right since microbore is going to provide resistance? Could the TRVs closing be a problem (there is a room stat too).

Thanks!

Ian · Moderator Joined: 18 Feb 2003 Posts: 32 Location: wigan

patrick · Joined: 13 Feb 2003 Posts: 7

Hi - Thanks for the next reply!

The heating tank is the same as the expansion tank - isn't it? I'm not sure if I have my terms wrong.

The feed into the heating system comes from the pipe from the expansion tank in the loft. The expansion tank is fed from the cold water cistern via a ball-cock. The cold feed and the expansion pipe connect onto the main boiler circuit at about 5" apart (ie. like a "U" shape). Does this match your description? I *think* this is as you describe - do you agree?

Thanks!!

Ian · Moderator Joined: 18 Feb 2003 Posts: 32 Location: wigan

Ian · Moderator Joined: 18 Feb 2003 Posts: 32 Location: wigan

patrick · Joined: 13 Feb 2003 Posts: 7

Hi Ian

A few more bits of evidence! Yes, the ball valve does shut off correctly - and I think that water is going out of the overflow due to the condendation of the steam in the header tank. I presume that this tank is meant to remain completely cold - there should normally be no flow up the expansion pipe into this tank unless something is wrong?

I've got around to unscrewing the cupboard around the pump and turned it down from setting 2 to 1 (3 is highest). Still hot water makes its way into the expansion tank, although I think that it is cooler. I guess that this would make sense since the pump is pushing the water less.

Dim question - could it just be that the pump is too big for the job? The radiators are on a 10mm microbore each with a TRV and a central thermostat too. Could there be a problem if there is a conflict between these - ie the central stat calling for heat but the TRVs shut down? There are of course 2 radiators operating as heat dumps. I presume that if the rads are not calling for heat then the 3 way valve should send heat to the hot water cylinder.

....do you think the problem is still with heat sensing? If so, I'll go and be more scientific and shut everything down for a few hours to cool so that I can perform the measurement that you suggest.

Thanks for your time, it is much appreciated! Very Happy

ChrisR · Posted: Sun Mar 02, 2003 11:11 pm Post subject:

First, I'm Not disagreeing with anything Ian is saying. Except that calling the Vent pipe the expansion pipe is a mistake. When the water expands on heating, 99% of it goes up the feed pipe, and the tiny bit up the vent. The water level in the two will be the same.

When (in your first post) you talk of "Overflow" do you mean the vent pipe - the one which goes up and over the tank? That is NOT an overflow!. The overflow goes off sideways to outside! There's a few red herrings here if we've got the wires crossed!
The water level in the header tank MUST never get anywhere near the overflow. There has to be sufficient room in the tank to accommodate all the expanded water. Otherwise you'll lose water when the thing heats and get new cold water in when it cools. That will kill your system with corrosion.

To put one of Ian's Q's more analytically - is the normal LEVEL of the water in the big (house tap water) tank, above that in the heating header tank? ie Are they both sitting on the floor of the loft?

Heat can be avoided in the header tank by making the feed pipe join the CH pipe from the bottom. What normally happens is that it joins from the top, so convection currents heat the pipe, then the tank. Even so , you shouldn't be getting steam in there. SO I'd agree that the boiler is getting the water too hot so it's boling, and the steam bubbles going up the vent pipe are causing the dripping - if it's from the vent and not from the overflow!!

In other words you have a boiler problem, which could have a lot of causes, like thermostat failure, pump problem, electronics (PCB) problem, etc.

patrick · Joined: 13 Feb 2003 Posts: 7

Hi - Sorry, my ignorance is showing all too easily!

I do mean by the pipe that comes in over the top of the tank that feeds the CH system (the vent pipe I think).

Both the cold store tank and the CH tank are sitting on the same surface: the level of the water in the cold tank is well above the level in the CH tank (12"?).

A pipe from the cold tank enters the top-side of the CH tank (ball valve).

The vent pipe above the tank does get hot - the water in this tank gets hot.

I've bent the ball valve to ensure that the water level in the header tank is low.

The pump is now on the lowest setting.

I don't hear any boiling water in the pipes.

Anything I can do to take this further? I guess simply turning down the stat on the boiler (Alpha range) to next to nothing?

Thanks - sorry if I have confused the issue.

Patrick

ChrisR · Posted: Tue Mar 04, 2003 8:49 am Post subject:

Water up the vent is due to overheatin, pipe configuration , or sometimes just a pulse when the pump starts.
When everyting is COLD, does water go out of the vent when you start the heating up?
See Ian's Q - how soon?

AGILE · Posted: Tue Mar 04, 2003 10:57 am Post subject:

Patrick, there seems to be a bit of confusion here. Perhaps I have missed something but from what I have read it is still unclear to me if the hot water is coming out of the vent pipe or not ???

There should never be "pump over", that is water coming out of the vent pipe. If it is then it should be adddressed quickly before the system sludges up.

Generally a normal system requires a 2 setting on the pump and a microbore needs a 3 setting on account of the increased resistance.

The level in the F & E tank when COLD should only be about 70 mm and will rise by up to 100 to 150 mm when the system is hot. It will be warm as the expansion takes place but cool down later and remain cold.

Does this help?

Tony Glazier

patrick · Joined: 13 Feb 2003 Posts: 7

Hi -

Hot water comes up the vent pipe (coming in over the top of the F&E tank) whenever the system is pumping. It does not stop or cool until the system is off.

ChrisR - sorry not sure what you mean "When everyting is COLD, does water go out of the vent when you start the heating up?" - does water flow into the F&E tank when the water is cold? The water is only cold when the system is off, so no water is flowing. Have I understood you properly?

Story so far Very Happy

The F&E gets warm and stays warm due to continuous flow up the vent pipe coming in over the top of the F&E tank. Ian suggested a couple of days ago that this is likely to be a stat problem somewhere - my assumption is on the boiler.

Does this sound right to everyone?

AGILE · Posted: Tue Mar 04, 2003 11:42 pm Post subject:

Good, now we know what the problem is!

Assuming the system was allright originally, the pump over will be due to sludge blocking the system. As new oxygen is introduced into the system every second it will not be long before you have the radiators all blocked up. I presume the water is a nice thick rusty reddish orange colour! There may already be a layer of soft sludge in the F & E tank.

The solution will be to flush out as much of the red sludge as possible and then treat with citric acid or similar chemicals to dissolve it. In my view better left to a professional who is experienced in this treament but I know that many people who use this site want to try everything themselves.

Tony Glazier
Agile Services

ChrisR · Posted: Wed Mar 05, 2003 5:52 am Post subject:

Patrick
We got there eventually! For this continuous pump-over, you must have a resistance in the pipe between where the vent pipe connects to the heating pipes and where the feed does. As that's only 5" in your case it is likely to be a hard deposit which will not clear easily. I'd start by cutting this bit of pipe out to have a look because it IS likely to be the worst area in the system. Sometimes the pipes look like hardened arteries -just a small hole down the middle, in which case you just cut back the pipe until you get to a healthy bit, and replace it. Then you'd do the flushing as Tony describes, followed by a corrosion inhibitor.