Help with pumping over on incorrect system layout (I believe!)

[uwavetv]

Hi

Would really appreciate if someone can help, done the 100 hrs on the web trying to fix myself but need guidance.

I have a two story house with boiler in external garage. I have recently added eTRVs on all but 1 rad, cleaned system etc. Issue is when I have only say three/four rads open the flow is poor through them and goes up and out the vent pipe (path of least resistance I assume) not as bad on pump setting 1 but on 2 it is a full flow out the vent. Pictures below, any way I can stop this, looked at combining the Vent and Feed but not sure where to join and also would have the filling air lock issue associated with this but would rather that problem than the circulation up the vent and down the feed.

Any guidance much appreciated
uWave

 

[Whyme]

Be very careful messing with the systems vent btw.

 

[kris]

its real simple if you look at your drawing, there's nothing stopping pumping over but if you moved the motorised valve next to boiler then , also little problem with vent as depending on the system , ie fully pumped the position of the vent is paramount I E teed off beside the boiler, the position it's in is per for Gravity but not fully pumped

 

[townfanjon]

Google close coupling ...... its a bit hard to explain on here, alter it to that , and it will be fine, somebody may help and put a pic up for you .

 

[kris]

Here DIY Heating Plumbing Tips 6 - Installation And Maintenance of The Circulator

 

[uwavetv]

Thanks guys
Kris, yes would move the motorised valve to boiler except I would need to bring the vent down to it and it is not practical as it is outside.
I will look into close coupling hopefully I will get somewhere...

 

[doitmyself]

The problem is caused by having the feed and vent pipes on either side of the boiler. This was OK when the boilers had low resistance cast iron heat exchangers, but a big no-no for a modern boiler with a high resistance aluminium or stainless steel exchanger.

Did you have an old boiler replaced within the past few years and have now got round to installing TRVs in place of manual valves? That could explain why the problem has only now occurred.

Which make/model boiler do you have?

The manual bypass should be replaced with an Automatic Bypass valve.

 

[Best]

Bypass valve should be beside the boiler, I think.
If the system is sound enough, oil or gas systems should be sealed type, which is a very easy conversion for a pro. That way, no open vents.
I see you are from N.I. Most heating systems over here were open vented and it is a common problem deciding how to prevent pumping over if altering the system or adding trvs

 

[lame plumber]

bypass should be as far away from the boiler as you can reasonably allow, to allow for some loss of heat on the circuit. Boiler mfis will give a minimum distance

 

[Nostrum]

I would simply cut and cap the existing cold feed where it tees into the bottom of the coil, and then tee into the flow as close as you can to the open vent after the tee piece.

No need to pressurise, you'll also do away with any potential blockage in the cold feed tee, should work just fine.

 

[Best]

Likely an oil boiler heating system and little odds if the bypass valve is closer to the boiler, as it won't do any harm IMO.
Combining the feed and vent pipe is preferable than it pumping over, if there is no other straight forward possibility, but I find systems with combined feed & vents absorb air and can have corrosion for some reason.
Take a good look at the sealed system option, as it is far superior

 

[uwavetv]

Thanks guys.. I have a Warmflow 90/120 boiler..in is in from new at house build in 2001..I added the trvs last year and suffered from overpump ever since..I have an abv purchased and planned to change out on drain down to fix this issue...on this I plan to install abv across the motorised valve at entry to coil instead of across coil that way if it has to operate it will dump heat into the tank..though it has just struck me that if this was continuous it may overhear the tank water as I assume if I was in CH only the tank stat would not be operational?? Any comments on this config? On the overpump issue I am a little uneasy about going sealed due to all the pipes buried in screed and potential leaks..perhaps I am being over cautious...

 

[Elgordo]

Better to place it across the coil , it could as you suggest allow too much flow to the cylinder and mightn't cure the pumping over , connect across cylinder before the mv and join the vent and feed pipe then dose with plenty of inhibitor !

 

[doitmyself]

I plan to install abv across the motorised valve at entry to coil instead of across coil that way if it has to operate it will dump heat into the tank

The ABV has to be:

1. Between flow and return
2. After the pump
3. Before any motorized valves

It can be installed either in place of the existing manual bypass valve or before the feed from the boiler divides to CH and HW.

An ABV is not there to dump heat but to provide a path for the excess pump pressure, particularly where TRVs are installed.

Compared to modern condensing gas boilers, your boiler's heat exchanger has a very low resistance. So the fact that the feed and vent connections are on different sides of the hex may not be too important. However the vent pipe should be before the pump (it appears to be after - assuming the pump is in the boiler). Warmflow would the best people to advise you.

In any case, the way the vent pipe has been connected will not help (I'm assuming the diagram is an accurate representation of the physical reality). This is because it is easier for the water to travel straight up rather than turn the corner to the valve. This can be overcome by moving the vent so it connects to a horizontal pipe.

 

[uwavetv]

OK 10:4 on abv I will put in t across the coil... If I try the combining as suggested above I will still have the vent after the pump but I am assuming that the combined now has the feed pressure from the header tank therefore more resistance than before and hopefully the flow will not be up the vent.(unless of course it needs to)
Again appreciating the help..