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I can see where you're coming from mate but I cant see how a slight restriction would cause the pump to vent over, seeing as the vent is within the neutral point of the systems margin. Of course I could be wrong.
To the OP. Is it hydrogen forming in the system, or hydrogen sulphide? The formation of the two happens for different reasons.
All I know is that the "air" coming out of bleeder valve smells of gas and is flammable so just assumed it's Hydrogen forming in system but don't know enough about that side of things I must say.
 
Both hydrogen sulphide and hydrogen are flammable. I believe hydrogen is odorless, whereas hydrogen sulphide smells of rotten eggs. Hydrogen is a by product of rusting and galvanic corrosion and hydrogen sulphide is due to bacterial issues so my understanding is, although chemistry is not my strong point.
 
I completely agree mate. If the OP can check this for us we at least know which direction to start heading in.
 
Thanks again guys fot the assistance!
Ok so I've just been up in the loft and got my daughter to turn the room stat up. There was no sign of any water movement. However when I got her to turn the stat down and turn heating and pump off hot water poured out the vent as you can hopefully see from the video.

Does this mean combining the vent and feed as suggested will resolve this issue?

Thanks again very much
 

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Well we've found the problem of air ingress and judging by the discolouration in the header tank the system is quite fouled.
@John.g why would this vent over only when pump deenergises?
 
The pump is located high up near the cylinder, also if there is a partially blockage restriction in the cold feed then the momentum of the water will quite possibly force the water up the vent.
Its also possible but unlikely with a OF boiler that there is pump overrun but with no ABV (automatic by pass valve) installed so the zone valve(s) close but pump continues on for a minute or so, leading to vent over.

Suggest the following, easiest one first but most unlikely..

Ensure pump orientation correct ie pumping towards the motorised valves.

Turn the cylinder stat down (after noting its setting at 60c or whatever) then latch it open manually, start boiler via roomstat if not already running, then stop it via roomstat and see if same problem persists.

Check that circ pump stops as soon as room stat switches off the boiler.


Combined vent&feed might help but there is a basic problem here which must be solved. I would ensure that the cold feed is absolutely free first of all.

Latching open a motorised valve will, in some cases. start the pump&boiler, so this test above may not work, I know that three Honeywell valves that I opened manually do not start up the system, probably a safety design as latching open these valves is supposedly to be used while filling the system.
 
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Pretty much what I was thinking mate. Water is constantly propelled out the discharge of the pump and drawn in on the suction. If the pump suddenly stops the water from discharge side has momentum but little is drawn in through a restriction and as water cant be compressed some takes the path of least resistance and straight up the vent.
 
Combining them is one possibility, as is your special the semi sealed. I personally would like to pressurise. However, we know what the problem is now and why the hydrogen is being produced, what the OP needs to do now is have a proper power flush and adequate inhibitor added. A power flush though is not a half hour job, its a day minimum and thats for small domestic dwellings. Once this has been carried out then the OP can consider how he approaches the outcome. Whatever method above choosen I would suggest a suitable filter for the system and appropriate means of air removal, free air, microbubbles and dissolved gases.
 
Combining them is one possibility, as is your special the semi sealed. I personally would like to pressurise. However, we know what the problem is now and why the hydrogen is being produced, what the OP needs to do now is have a proper power flush and adequate inhibitor added. A power flush though is not a half hour job, its a day minimum and thats for small domestic dwellings. Once this has been carried out then the OP can consider how he approaches the outcome. Whatever method above choosen I would suggest a suitable filter for the system and appropriate means of air removal, free air, microbubbles and dissolved gases.
Thank you very much guys
I will try out the suggestions asap.
I can confirm the pump is the correct way with arrow pointing towards the 2 port valves.
I'll update you on the little test suggested first then later on when I get the system flushed out etc.
Thanks again. 👍
 
To add to John's comment. Like he said the manual switch on motorised valves is primarily for filling and some two ports ie Honeywell the manual lever won't start the boiler. However if you take the head off and use a wooden peg you can close this circuit to bring the boiler and pump on. Ive never done it but remember an associate saying it could be done (allows you to bring boiler on if the programmer is not accessible, for whatever reason).

I suspect if the blockage is where we think it is then the pumping over will happen whenever HW or CH is shut down.
 
Just a quick related point:
I noticed the 15mm feed has a gate valve at pump and isolating valve at header tank.

1. When it comes to combining the vent and feed as has been suggested, does this mean I need a shut off valve at bottom also in addition to an isolating valve in loft to tank?

2. Does this also mean I when it comes to doing away with the 15mm feed I can simply shut off the gate valve or is that bad practice incase valve fails etc?

Thanks very much again!
 
If you're combining it there should be no valves in any vent pipe for obvious safety reasons. Come out of bottom of header tank in 22mm and tee into the vent, the vent then continues to rise up and over the header tank, with 450mm minimum between water cold fill line and top of vent u bend. You can then blank off where the old fill entered the system.
There are other options though as I said above but the primary job is getting the system cleaned.
 
To add to John's comment. Like he said the manual switch on motorised valves is primarily for filling and some two ports ie Honeywell the manual lever won't start the boiler. However if you take the head off and use a wooden peg you can close this circuit to bring the boiler and pump on. Ive never done it but remember an associate saying it could be done (allows you to bring boiler on if the programmer is not accessible, for whatever reason).

I suspect if the blockage is where we think it is then the pumping over will happen whenever HW or CH is shut down.
The pump over may not happen when one zone valve shuts as there is somewhere for the flow to go but would be another test to add
Just a quick related point:
I noticed the 15mm feed has a gate valve at pump and isolating valve at header tank.

1. When it comes to combining the vent and feed as has been suggested, does this mean I need a shut off valve at bottom also in addition to an isolating valve in loft to tank?

2. Does this also mean I when it comes to doing away with the 15mm feed I can simply shut off the gate valve or is that bad practice incase valve fails etc?

Thanks very much again!
Just shut the cold feed make up where it joins the vent.

You can also let the cold feed isol valve in place at the tank, just give it a good flush into a bucket before connecting up. You cannot have a isol valve where the cold feed also acts as the vent , ie no "vent"

Also T in the cold feed as close to the header tank and Vent as you can (see my set up)
 
I ment the pump over could happen if either CH or HW were on on their own and demand stopped, if the restriction is where we believe it to be.
 
If you're combining it there should be no valves in any vent pipe for obvious safety reasons. Come out of bottom of header tank in 22mm and tee into the vent, the vent then continues to rise up and over the header tank, with 450mm minimum between water cold fill line and top of vent u bend. You can then blank off where the old fill entered the system.
There are other options though as I said above but the primary job is getting the system cleaned.
I would be inclined to do the combined job before system clean (obviously flush out the F&E tank through the cold feed isol valve at the tank when disconnected) as an oil fired boiler Hx is just basically a steel box of water which won't easily get choked, the system can then be cleaned/flushed out at ones convenience especially if the pump over/air ingress problem is now solved.
 
The thing is mate and im not saying the system is this bad but I once attended a job, oil fired external with vent teed in after the pump. It was constantly pumping over whilst in operation (not the case here, so obviously less air ingress) but the system was so bad that every inch of the system was riddled with sludge, throughout most of the 22mm system it had an internal bore of 2 or 3mm max and im not exaggerating. The boiler was just as fouled.
Where as I agree combining the two might fix the pumping over I really don't think flushing the system should be ignored. The quality of water, its cleanliness and the amount of oxygen all affect its conductivity, its PH value etc etc, all of this can add to serious corrosion if not addressed.
Have a read up on VDI 2035 water treatment. Its a technical standard in Germany, not over here yet but explains what I said above and really should be used of here.
 
Thanks again.
Just to be clear I realise more is involved than simply combining to he vent and feed and will apply the other points. Just needed to get this side of things clear in my head.
I noticed there is another plastic kinked 15mm pipe done away with behind emersion to perhaps this is why they fitted a gate valve at pump for everything the pipe clogs up maybe 🙄

I've made another sketch as to what I think you are telling me 😃

Probably got it wrong again and apologise if so.
I'm keen to learn at least 😊
 

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That's it, no isol valves on the vent but you may leave the isol valve on the cold feed , if a gate type, (with wheel) as there is practically no resistance in this when fully open. You can also leave the isol valve where the cold feed was/is teed in to the vent and just close it, can always remove it when carrying out system clean later.
Is the vent actually passing up adjacent to the cold feed at the header tank, as shown?, if so a very easy task to tee in.
 
That's it, no isol valves on the vent but you may leave the isol valve on the cold feed , if a gate type, (with wheel) as there is practically no resistance in this when fully open. You can also leave the isol valve where the cold feed was/is teed in to the vent and just close it, can always remove it when carrying out system clean later.
Is the vent actually passing up adjacent to the cold feed at the header tank, as shown?, if so a very easy task to tee in.
Great thanks John
Yes the vent is running right next to cold feed at tank so will be very straight forward.

Ta
 
Just wanted you thank you all for the assistance given.
I flushed out the system after combining the feed and vent in the manner suggested. I decided to use a 28mm gate valve below tank reduced to 22mm so as to minimise any restrictions for vent when open.

The header tank was so badly fouled I ended up removing it to give it a thorough clean outdoors.

I also added a magnacleanse filter on the return to hopefully minimise such a build up again along with inhibitor.

The end resulted speak for themselves. Pipe to tank is warm until about a meter below tank where it is stone cold.

No venting when pump stops anymore.

Really happy with the outcome and not possible without the expertise given here.

Thanks a million 😊
 

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