improving pipework for feed and vent

[ScottishGasMan]

i haven't really balanced the rads. much because i'm worried about restricting the flow incase it makes more pumping over, i also don't think i have a bypass valve so a bit worried about safety

Bypass has nothing to do with saftey, and is not required on a Y-plan where there are radiators that do not get turned off.

Pumping over can not happen regardless of the radiator restriction if your feed vent and pump are fitted correctly.

 

[Hugh Jaleak]

Classic signs (in my opinion) of a circulation problem. Was the system cleaned when the new boiler was fitted?

I'd be sorting those affected sections of pipework, then give the system a bloody good clean before doing anything else. Once you've got the blocked sections of pipe sorted, put some Sentinel X400 in and leave that circulating for a few weeks, then drain out, and flush through the system and see what happens then. You're tinkering around the edges instead of getting to the heart of the issue. Its an old system, badly maintained in the past, you may be surprised what a good clean out will do.

Clean water wont turn black as you describe in 2 weeks just because you've not put inhibitor in. Its done that through stirring up all the crud already lying in the system. You cant just clean bits out, e.g. rads, the whole lot needs to be flushed through to achieve anything. If the system is clean then the water will be able to circulate as it should, and you can balance the system according to get all the rads hot.

As long as one rad is open fully to provide a path for water to flow if the TRV's are shutting down then this will act as a bypass.

 

[ScottishGasMan]

Also, is the pump powered from the boiler? Does it run on after you turn the heating and hot water off?

 

[Razor900]

As several people have told you in this thread the problem is a restriction in the cold feed pipework which is allowing the circulator to pull air down the open vent. You can either tee the feed into the vent or clean the pipework

 

[chris5346]

hi all , thanks for he info.
yes when the new boiler was fitted the installer ran F3 through it for a couple of hours, i have also repeated the same last year and kept it in for about a week but i found the water that came out looked the same as when it went in, i did try to switch off rads and clean one at a time but i'm not sure if i kept the water side open so maybe i was just cleaning the hot water side, at the same time i removed all the rads and poured boiling water through them and made sure they were clean as poss. without power flushing them.
when i re-tested the system i didn't put inhibitor in straight away because i also had a plan to fit a new larger modern rad in the hall, so when it was running for about 2 weeks along with the air bubbles in system the water went very brown and light brown sludge formed in the filter, so i have cleared that all out this summer and fitted new rad in hall and added inhibitor this time.
the pump is an alpha 2L i think it's a 5M head ? and the old pump was a wilo smart maybe 6 M head ? at the time i didn't realise what i was buying and may have under rated it ?

 

[chris5346]

i know i have been avoiding investigating the feed connection and making mods around the boiler but it's in a tricky position and i don't have any soldering equipment. i just do what i can do.
there's been a lot of alterations and it's difficult for me to know what's causing what.
also i used to get terrible noises in the pipework , luckely this year i managed to find some pipework that was pinned to a joist with a nail , so i have freed it up and wrapped wadding around and it's much better , i have also made some improvements where pipes fit to the rads.

 

[Nige F]

hi,
yes if i get a magnet there is a small attraction to it at those tee's but i don't think they are badly blocked ?
what about not having a bypass valve ? are they just a safety thing or do they help the system work better ?

You are thinking wrong my friend - I have just renewed the feed/vent on my system at home - it was 80% blocked and yet there was just a small attraction to a magnet - you're not sticking the magnet to steel , just an oxide- believe me and the other guys, they block badly PS I think 4a is better

 

[chris5346]

hi, well i'm going to cut it out and take a look, i'll post a photo next week,
many thanks for all your replies,

 

[chris5346]

yes the pump does have an over run , i think it is 10 mins but it seems to vary ?
i need to check and take some measurements.
i'd be happy to run the pump all the time if it helps ?

 

[ScottishGasMan]

yes the pump does have an over run , i think it is 10 mins but it seems to vary ?
i need to check and take some measurements.
i'd be happy to run the pump all the time if it helps ?

No need, just making sure the pump is wired to the boiler to provide an over run of some sort. People skip this a lot on these set ups and can cause all sorts of damage and issues.

 

[chris5346]

yes it definately over runs , usually around 5 mins it seems to vary with the temperatures.
the boiler and pluming was fitted by one guy and the electrics the next day by another guy - both worked for the same company.
they basically just got it working and that was it as far as they were concerned.
think i'll start work on it monday and see what that feed pipe is like and decide what's best to do from there.
what about the airing cupboard plumming i recently raised the pump a foot because it was touching the floor and i couldn't get a spanner on the bottom nuts - could that be a mistake and make the system worse ?
here's a before and after

 

[Nige F]

No problem with that at all

 

[D_Hailsham]

How far is the "bend" in the vent pipe above the water level in the F&E tank?

It would be better if the vent and feed pipes were both coming off the horizontal pipe, i.e moved to the right in the current layout. In the current arrangement, with the vent pipe a straight vertical run there is much less resistance compared to going round the bend, so water will want to go straight up.

Balancing, done correctly, will reduce the need to have the pump running fast. Contrary to what many think, water does not have to be "pushed" through a radiator; it goes through naturally because the pressure at the return connection is lower than the pressure at the flow connection, i.e. the water is "sucked" through the rad.

You don't need a bypass as you have a mid-position valve which means there is always an open path for the water to circulate.

 

[chris5346]

hello, that's interesting,
the vent pipe that goes up and over the F and E tank is around half a meter, when it was pumping over i did used to experiment by changing the height of it.
what i will probably end up doing is re-using the 22mm copper pipe that's already in place for the vent and either use it for combined feed and vent or just re-use it for the vent.
i will cut out the Tee's hopefully tomorrow and see what they are like inside.
yes i do need to start balancing the system because i think what's happening is the heat goes through the bathroom rad and back on the return to the boiler before the rest of the heat gets around the house causing over temp and hot pipes around the boiler, but whilst i have been getting air and pumping over problems i like to keep lockshields fully open.
this is what i was thinking of doing :

 

[DP]

I would leave the Feed and vent as is, filter can be fitted where shown current layout (but better on the return (if anyone doubts, check Megnaclean installation sheet)

I woukd also look at the pipe between vent and feed n the flow

Why is the filter so low near the floor?