Hot water venting into header tank, this issue not covered on previous posts

[centralheatking]

Thanks guys.

Yes there is an immersion fitted, but it's never used.

JohnG and EvilDr, ok I could try that, you think the water is travelling too fast through the coil whereas I was thinking it was flowing too slow! I could try to use the red gate valve as a balancer and restrict the flow with that one, if that fails I will drain down and fit a different valve there.

Thanks.
[automerge]1573139534[/automerge]
Just tried setting pump speed to 2, and adjusting the red gate valve further and further closed in increments, I'm afraid the water never stops coming out of the vent unless the gate valve is closed fully, which of course knackers the boiler.. back to pump speed 1 and all is ok again, so it doesn't seem that throttling the cylinder coil makes any difference.

so where is the immersion and cylinder on the diagram just curious
centralheatking

 

[karlrich1]

You must currently have a positive pressure on the vent and negative on the cold feed and a similar (slightly less) resistance to that of the DHW circuit, if that makes sense?

I would alter the pipework to suit the following diagram. This is how we always piped open vented systems. You should have a neutral point in the system where the cold feed enters. If the vent connection is within the right distance and the height of the F&E tank and the vent are good, then there must be a reason why there is a pressure difference between those two points which is enough to cause circulation.

If you don't cure it by doing this, then there is obviously another cause but in my opinion you are better to rule out the possibility of it being something as simple as pipework configuration.

Note: Cold feed is inverted.


View attachment 41360

OK - thanks, the only difference between this diagram and my installation is the inversion of the cold feed. Both my cold feed and vent attach to vertical pipe through standard 90 deg elbows, neither have a negative loop in them. Does the cold feed inversion make that much difference?

 

[Last Plumber]

If you was going to start messing with pipework though I'd just change it to a combined Feed and Vent. That'll sort the issue.

You could try that. It's not something I have ever done or thought a good idea but that's my personal view on it. I know people who do that and it works for them.

You could also change it to a sealed system provided the Boiler and system components are up to it.

It could be one of many things. De-zincification in the bottom connection of the brass tee where the cold feed enters could create a restriction enough to cause this issue. You need to start somewhere.

Maybe pull that section of pipework to bits and look inside, there could well be a restriction between the vent and cold feed connections.
[automerge]1573142281[/automerge]

OK - thanks, the only difference between this diagram and my installation is the inversion of the cold feed. Both my cold feed and vent attach to vertical pipe through standard 90 deg elbows, neither have a negative loop in them. Does the cold feed inversion make that much difference?

I have known that to make a difference yes. I can't explain why but I can't say I have given it a great deal of thought.
Have you looked in the tee? and between the vent and feed connections?

 

[karlrich1]

so where is the immersion and cylinder on the diagram just curious
centralheatking

See pics attached. Immersion is in the top of the cylinder.
[automerge]1573142577[/automerge]

You could try that. It's not something I have ever done or thought a good idea but that's my personal view on it. I know people who do that and it works for them.

You could also change it to a sealed system provided the Boiler and system components are up to it.

It could be one of many things. De-zincification in the bottom connection of the brass tee where the cold feed enters could create a restriction enough to cause this issue. You need to start somewhere.

Maybe pull that section of pipework to bits and look inside, there could well be a restriction between the vent and cold feed connections.
[automerge]1573142281[/automerge]

I have known that to make a difference yes. I can't explain why but I can't say I have given it a great deal of thought.
Have you looked in the tee? and between the vent and feed connections?

Not yet, was trying to sort without draining the system down for a third time this week, but I will get round to that, I could put an inversion in there at the same time.

 

[John.g]

Thanks guys.

Yes there is an immersion fitted, but it's never used.

JohnG and EvilDr, ok I could try that, you think the water is travelling too fast through the coil whereas I was thinking it was flowing too slow! I could try to use the red gate valve as a balancer and restrict the flow with that one, if that fails I will drain down and fit a different valve there.

Thanks.
[automerge]1573139534[/automerge]
Just tried setting pump speed to 2, and adjusting the red gate valve further and further closed in increments, I'm afraid the water never stops coming out of the vent unless the gate valve is closed fully, which of course knackers the boiler.. back to pump speed 1 and all is ok again, so it doesn't seem that throttling the cylinder coil makes any difference.

Why does shutting the balancing valve knacker the boiler if both CH&HW are selected?? as you said earlier that when CH only was selected on speed2 then everything was OK with no pump over or boiler problems as shutting off the balancing valve with both CH&HW selected is the same as having CH only selected?, excepting some problem with the 3 way valve?.

Are the rads heating up ok on speed1 IF CH only selected? and is the boiler "normal"?. If so then have you tried it on speed1 with the cylinder coil throttled in to ~ a 1/2 turn opened with both CH&HW on, if still ok then see if no pump over on speed1 with HW only selected.

 

[karlrich1]

Why does shutting the balancing valve knacker the boiler if both CH&HW are selected?? as you said earlier that when CH only was selected on speed2 then everything was OK with no pump over or boiler problems as shutting off the balancing valve with both CH&HW selected is the same as having CH only selected?, excepting some problem with the 3 way valve?.

Are the rads heating up ok on speed1 IF CH only selected? and is the boiler "normal"?. If so then have you tried it on speed1 with the cylinder coil throttled in to ~ a 1/2 turn opened with both CH&HW on, if still ok then see if no pump over on speed1 with HW only selected.

As the issue only happens when the HW is on (seems to be completely independent of CH on or off) I was seeing how closed the valve needed to be to stop the overflow with HW on only. You are correct if CH was on the boiler would be fine - but during my test I was restricting flow to the boiler.

Yes that is what I have tried now. Pump speed 1, cylinder coil throttled to one turn open. Boiler is OK, Rads are ok, no overflow through the vent. I need to try again in the morning from scratch as the house is already warm and we have a tank full of hot water, so I can't tell just yet if the heat up rate of the rads is acceptable or not! My wife will inform me of that first thing in the morning.... I'll report back soon.

Many thanks for all of this.

 

[John.g]

How is your system performing since change?.

 

[karlrich1]

How is your system performing since change?.

Still not great really, pump speed 1 means the boiler is cutting out regularly due to temp difference between in and out, also the rads on cold days don't seem to get up to temperature quickly or stay there. I have also had a few instances once everything has gone off of a water surge up the vent into the header tank and out through the overflow into the garden.

So I have run a Sentinel x800 through the system over the weekend and today I am going to disassemble what I can around the vent and cold feed area, replace the 3 port valve (I bought a non honeywell version so we will see how that goes) and see if I can see anything new.

Will report back later today.
[automerge]1574086754[/automerge]
New 3 way valve fitted. Most of the pipe work boiler side of the pump was blocked by about 50% including the tee for the vent, the blockage didn't go much further south than this and was also clear either side of the Y valve. Pump inlet and outlet around 30% also blocked with black residue.

Took it all apart (compression fittings only) cleaned out the pump and pipework as best as I could and refitted. After several hours of bleeding the system is 'relatively' happy, in that there is no longer any water coming out of the vent, regardless of CH/HW selection or pump speed.

There are still problems however, one of my rads (bathroom) I cannot get hot for love nor money, throttling back all other rads just creates too much of a restriction somewhere and the boiler has a hissy fit and shuts down in seconds. All other rads are getting hot fine. So there must still be an airlock somewhere, or another restriction/blockage in the CH pipework restricting flow. Or my boiler settings are just plain wrong for my house.......

Same happens if I select pump speed 1 and all rads are throttled normally, boiler heats up too quick and shuts down.

One step forwards - 2 steps back!

 

[John.g]

You may find that the pump ports & pump impeller are now full of crap as well, if you shut off the pump isolation valves you should be able to remove the pump head to clean out the impeller and while the head is removed you should backflush the pump ports by alternatively opening/shutting the isolation valves although you did say above that you cleaned it out as best you could.
I hope not, but there is now a possibility that the boiler HX is partially blocked as well, when you do sort it out you might consider fitting a magnetic filter before the boiler inlet, if one not already fitted.

 

[karlrich1]

You may find that the pump ports & pump impeller are now full of crap as well, if you shut off the pump isolation valves you should be able to remove the pump head to clean out the impeller and while the head is removed you should backflush the pump ports by alternatively opening/shutting the isolation valves although you did say above that you cleaned it out as best you could.
I hope not, but there is now a possibility that the boiler HX is partially blocked as well, when you do sort it out you might consider fitting a magnetic filter before the boiler inlet, if one not already fitted.

yes - the pump ports I have cleaned as best as I can. the pump impeller was new only a year ago along with a power flush. Can I do something about the boiler HX? (I have a Vaillant ecoTEC plus now) I do have a magnaclean unit fitted, I have cleaned this out a few times over the past 2 weeks and from there being a fair amount on there to begin with it's been relatively clean since then. I think I am suffering ultimately with a cascade and ***ulative affect of bad jobs - I have a mishmash of 15mm and microbore installed already when I bought the house 15 years ago (the bathroom rad is on the latter) and when I first moved in the plumbers who fitted the new boiler in the garage (back boiler in the living room exploded 2 weeks in to my new residence) re-jigged the system and managed to get a couple of pipes mixed up - nonthewiser 4 years later this came home to roost with a completely blocked system which knackered the Worcester Bosch boiler completely. A lot of the microbore is under concrete flooring so I can do little about that, but I guess in the spring I can try to replace some of it. Failing that I am out of ideas.