spluttering from vent pipe when pump start/stops

[puzzlebobble]

Hi, I was hoping for your advice on something I've noticed.

My system is:
Potterton suprima 100 (fairly recent new PCB).
pump: grundfos super selectric. (set to 3)
Open vented
separate vent and feed (vent is 22mm).
two honeywell zone valves - both two way
automatic bypass (set to 2)

Problem is: when hot water is on in the morning there are splutters from the vent to the feed/expansion tank. Having observed the system what appears to happen is that the boiler turns off presumably because the water leaving the boiler is hot enough. The pump continues to run. After a while the boiler starts again- just before it does this the pump stops and restarts. When it does this there is a splutter from the vent. There is also quite a lot of banging during the period of time the hot water tank is being heated. I think the banging sounds like it could be coming from the region of wall where amongst others the feed and expansion pipe are.

I assume the same is happening when the heating is on but because the boiler turns off/on less frequently i haven't noticed it.

Known problems with the system
1) automatic air vent by boiler doesn't work (in post)
2) zone valve to hot water tank- lever does not turn although with the box off full movement of the spindle is seen and the return pipe from the hot water tank gets hot quickly (also in post)
3) pipes in loft have fairly long (3m) horizontal region and may even be slightly down hill to tank. Have had problems with air locks in both central heating and cold water systems. There may be another horizontal segment between 1st and second floors too.

I think the problem may be occurring since I put the auto bypass in and turned the pump up to 3. To get the required flow to the boiler (4.5l) it seems to me from the curves that it has to be on three.

2 questions:
1) is it normal that the pump turns off and on before the boiler relights?
2) what do you think the problem with the system is?
3) the small cylinder which takes the flow from the boiler, has the vent pipe coming out from the top and the flow to the pump near the bottom- is it more complicated than it looks of just a cylinder with three appropriately positioned outlets? and can they go wrong?

Many thanks for any advice you've got!

 

[twgas]

3) the small cylinder which takes the flow from the boiler, has the vent pipe coming out from the top and the flow to the pump near the bottom- is it more complicated than it looks of just a cylinder with three appropriately positioned outlets? and can they go wrong?

probably a blockage in this, air seperator,

 

[puzzlebobble]

Hi Mick,
thanks for your help. Can I just check that this is an air separator:

For my own interest how would it being blocked cause the spluttering when the motor stop/started and what would it look like if you opened it up? Would it just be sludge blocking it? I've got some sentinel x400 sludge remover but someone told me not to use it as it can cause leaks.

thanks for any advice!

 

[seco services]

never had a leak from it and use it on powerflushing all the time.

not a diyer by any chance ?

 

[Softus]

Can I just check that this is an air separator:

It is, but judging from that soldering attempt it's full of solder and flux.

 

[puzzlebobble]

sludge remover in. It was a diyer at work who told me that- had a theory about leaks being plugged by limescale and then when you added the sludge remover they opened up.

I think the system was installed in 1996 when the boiler was but I'm not really sure. If solder/flux got in back then could that explain the symptoms now? maybe was a bit bunged up with flux and then some sludge tipped it over the edge?

Hopefully the sludge remover will do the trick. Are there any other causes of the problems I've got that I should consider?

Thanks all!

 

[Softus]

sludge remover in. It was a diyer at work who told me that- had a theory about leaks being plugged by limescale and then when you added the sludge remover they opened up.

He's half right about the minority of systems.

The half right part is that latent leaks can be covered by sludge and flakes of rust that are dislodged in the cleaning process. The half wrong part is that closed systems don't contain limescale.

Leave the chemical in for a few days (at least), and during that time make sure that each radiator gets nice and hot.

 

[puzzlebobble]

will do softus. thanks

 

[jeffreyw]

1,check out feed and vent to see if they are within 6 inch apart
could be dragging air in
2,check hight of vent pipe needs to be 1m above tank
3,check bend in vent so it creates air vacuum
4,pump speed
5,is water in tank redhot and coming out of overflow
6,over heating of system
just a few suggestions

 

[puzzlebobble]

thanks jeffrey for your alternative suggestions. I'm still hoping it's a blocked air separator and the sludge remover does the trick but it's good to have some other ideas.

"1,check out feed and vent to see if they are within 6 inch apart
could be dragging air in"

vent is about 4 inches above water level of feed tank.

"2,check hight of vent pipe needs to be 1m above tank"

The arch of the vent is about 40-50cm above the water level but has been so for over 10 years.

"3,check bend in vent so it creates air vacuum"

The vent runs from near the feed pipe up the side of the tank, arches over and the turns downward into the tank.

"4,pump speed"

pump needs to be on III as the boiler requires 4.5l/min minimum and there are 18 radiators. Maybe the combination of turning the pump up to III and th vent only being 50cm above feed?

"5,is water in tank redhot and coming out of overflow"

no the fluid spluttered is warm but the tank is cold and not in overflow.

"6,over heating of system"

I don't think so. The boiler seems to be turning off and on to keep the correct water temperature normally; there's also an overheat thermostat which would 'lock out' if it tripped.

Could it be that because of the faulty AAV there is some air in the system which is compressed when the boiler is running but when the pump stops it expands and pushes water up the vent?

Or could a narrowing in the feed pipe cause this problem?

 

[Softus]

1,check out feed and vent to see if they are within 6 inch apart
could be dragging air in

IMHO the cold feed joins to a reduced end tee just after the air eliminator.

2,check hight of vent pipe needs to be 1m above tank

Why oh why oh why do you think it needs to be 1m above the cistern?

3,check bend in vent so it creates air vacuum

What?!

4,pump speed

What speed are you recommending?

 

[puzzlebobble]

yes Softus, I believe that is the cold feed. I haven't seen the pipes where they run up behind walls but there are no other pipes which could really be the cold feed.

 

[puzzlebobble]

Hi, it's been two weeks since I put the sludge remover in. Thankfully no leaks but still the same problem; if anything it's gone from a splutter each time the pump stops to a dribble.

There has been a new finding though. As suggested I went to check all the rads were getting nice and hot and found air in the top floor rads. There didn't used to be this problem before I last drained/refilled the system.

I guess that this means the system is sucking in air when the pump starts and putting out water through the vent when it stops? Given that the cold feed tank is several metres above the pump and the feed tank inserts nearer the pump I would have thought that if anything is sucked in when the pump starts it should predominately come from the cold feed? As this doesn't happen could it mean that (since the system was refilled) there is a blockage in the cold feed pipe?

Swinging a magnet around the pipes in the airing cupboard it likes the horizontal part of the feed pipe (pic above) before it tees into the pipe from the air separator. It isn't attracted currently to the air separator.

So my hypothesis is that there is magnetic stuff blocking the feed pipe at this point and that the sludge cleaner hasn't removed it because water doesn't circulate in this part of the system.

Before I start cutting pipes it'd be nice if any of you could offer your opinion as to whether I could be right?

Also another quick question- I might be being dim but the AAV by the boiler is bust and I was going to replace it at the same time. The old one is on the flow from the boiler to the pump- wouldn't it make more sense to have it on the flow from the pump to the boiler?

 

[puzzlebobble]

I won't be the least bit offended if I'm told to stop being crazy and to "put the hacksaw down!"

 

[JohnD]

the magnet has found some magnetite sludge (black). If you have brown sludge (rust) this is almost undetectable by magnet. however you will see it as brown mud in the bottom of the F&E.

If you are using X400 you will be able to see it is working if the circulating water goes jet black (this is with black deposits that it has started to break down so they circulate in the water)

True there is little movement in the cold feed except a bit of expansion and contraction each day as the system gets hot and cold. I have an idea it might only be a litre or so a day.

If you have a blockage in the cold feed it is usually necessary to cut it out and put in a new bit of pipe. Sometimes if you can open it you can poke it clear with wire. The fragments of black can be hard though, so will not do your pump any good, but will break down with X400.

It is difficult to get a wet pipe dry enough to resolder but you can use compression fittings if you don't mind plumbers sneering at you and this will make it easier to open if it happens again.

If your system has been splashing and gulping it will have drawn air in which encourages brown rust. When you have sorted it out, be sure to add an inhibitor such as X100.

You can leave the X400 in for up to four weeks before draining and flushing. If you decide you have a black sludge problem you can fit a Magnaclean which will cost you about £100 but is very satisfying when you empty out all the black sludge it has trapped from the circulating water.

I am just a householder