Hot water flowing from vent pipe into loft tank

[wardr77]

Just to update:

After a couple of days with X400 in the system the pump over has stopped on pump setting 1, but the water in the f&e tank is still luke warm which I'm not sure I understand. I stared at the vent for a good while and deffo no water coming from it. I then changed pump setting to 2 and water started coming out of vent again. Just for info I put my thumb over feed hole in the tank and the water stopped coming out of the vent, when I removed thumb out came the water again, no idea why i did this or why I mention it, but maybe of interest! So i guess X400 has helped clear some sludge, but will still require pipe cutting / stick poking to fix the problem once and for all!
Just to note I will be leaving the X400 in the system for a couple of weeks before flushing the system

 

[wardr77]

Also think I've just figured out why the water is still warm. Took the thermostat up in the loft. I turned up the heating and the pump switches on, I hear a gurgling coming from the vent pipe but no water, when I turn the heating down and the boiler switches off a quick blast of hot water comes out the vent.

 

[Madrab]

stick poking

......

 

[BlueLoo]

Also think I've just figured out why the water is still warm. Took the thermostat up in the loft. I turned up the heating and the pump switches on, I hear a gurgling coming from the vent pipe but no water, when I turn the heating down and the boiler switches off a quick blast of hot water comes out the vent.

Momentum stop causing water hammer which finds the weakest link in the system and you get the vent "burping" ?

I thought the cleaner would get the system moving somewhat. Good news.

I'll repeat my suggestion to remove and flush the rads when you drain down.

I wonder how dirty the magnetic filter will be?

 

[wardr77]

 

[wardr77]

Not great, that was clean on sunday!

 

[fixitflav]

ut the water in the f&e tank is still lukewarm which I'm not sure I understand.

As I said in #102
The cold feed should preferably have a U-bend and come into the bottom of the pipe run. This is to avoid convection warming the water in the F/E tank, which encourages algae growth.

Presumably you will leave the pump on setting 1, if everything is OK at that speed.

 

[Madrab]

That's not bad considering how bad it could be ....

When you bleed a radiator, how clean is the system water? Is it quite clear?

 

[Dereekoo]

Not great, that was clean on sunday!

Actually it is great, it shows the crap is moving and the filter is working

 

[wardr77]

That's not bad considering how bad it could be ....

When you bleed a radiator, how clean is the system water? Is it quite clear?

Yes, that's bad! When bleeding the radiators the water is clear, the few I have taken off and blasted through had a fair amount of brown/ black sludge in them

 

[Gasguru]

Forget the water quality when bleeding rads...it means nothing.
Your F&E cistern is getting warm due to the pumping over...it's acting like a radiator. IIRC the feed connection is downstairs so you might expect after some time a little heat to rise through the pipe from convection but it would be negligable. Where the cistern is close to the system then an inverted connection (a heat trap) is advised as previously mentioned to stop convection.
The slug if water pumping over when the demand stops is probably due to the zone valves slamming shut and the bypass opening...ie. all of a sudden the system is a much shorter loop.
You've mentioned a 30kW CDi and 19 rads...you'll almost certainly need to run that pump on speed 2 or more to ensure all rads heat fully and the temperature drop across each one is no more than 15 or 20 degrees...there's significant head loss (friction) with that boiler.
If you're determined to continue with the cleaner try increasing the vent loop height as high as possible....at the moment all that circulation through the cistern is oxygenating the water and very detrimental. A speedfit bodge will suffice for now.

 

[BlueLoo]

That's not bad considering how bad it could be ....

When you bleed a radiator, how clean is the system water? Is it quite clear?

Crikey

 

[BlueLoo]

Yes, that's bad! When bleeding the radiators the water is clear, the few I have taken off and blasted through had a fair amount of brown/ black sludge in them

I was stunned when i did mine.
Amazeballs

 

[wardr77]

Thanks gasguru, the pump over is not happening on setting 1 now, I think the warm water is due to the blast of water everytime the boiler shuts off as it maintains temps. I guess this is still pump over but at least it not continuous as before. I know I need to replace the vent / feed section , it's just whether I'm brave enough to attempt it myself or not! Either way it will be in jan now.
Ref the vent pipe height it's way over 300mm and located in the highest point of the loft so no possibility to extend (chalet bungalow with not a lot of loft)

 

[wardr77]

Hi Just to provide a final update on this. The section was cut out and replaced today and I'm glad that I did so; the 15mm feed was almost blocked, the pipe between the feed and the pump inlet had 3-4mm thick scale around it and the 28mm pipe section between the vent and the feed was worst of all and was reduced to around a 10mm bore. The magnetite was firmly fixed to the pipe and would not have been easy to remove with the pipe work in situ. The plumber did connect the feed to the vent just above where the feed would normally join the pipe to the pump inlet. But happy to report no more pump over into the F&E tank on all pump settings. Thanks again for all your help and support here which enabled me to make the right decision for this particular problem!