Adding MagnaClean To Flow - Two Pipes On Return

[JackK]

I have a open vented heat only boiler and a vented indirect cylinder

The fand e tank has the three connections you mentioned.

I would expect there to be discharge from the vent pipes but I would never expect water to come back down from the discharge pipes. They are higher than the top of the fande cylinder and not touching

It definitely seems like when mains cold and hot is mixed the brown water comes down and is aggitated

Before I change the tap I want to understand how this is possible and where the brown water is coming from

 

[Madrab]

I would expect there to be discharge from the vent pipes

In normal operation, there shouldn't be any discharge from the vent pipe, it's there as a safety release. If there is it means it's pumping over and that's indicative of a restriction that and it can also oxygenate the system water, that is drawn then down the feed pipe and into the system and that accelerates corrosion, hence the brown water.

As far as positioning the pump is concerned then as we know with an open vent the pump needs to be in a certain position relative to the feed and vent to ensure that the systems isn't put under either negative or incorrect positive pressure. If the pump is 'just moved to the flow' in this scenario then that may cause problems unless it'[s know where the feed and vent are positioned.

 

[JackK]

Here is a picture of the hot water drain off from cylinder - I am convinced that the white steel pipe serves only the downstairs kitchen hot tap and the bath / basin on first floor is from the copper after the gate valve.

I still would not expect there to be brown water from kitchen hot water tap

 

[Madrab]

Hot water drain off, do you mean the hot water supply pipework? Are you talking about the large piece of copper in the foreground coming in from the left and heading into the iron and that heads down in iron and up in copper (probably the vent) and then tees off a little higher up and heading down, through the red gate valve?

You are getting brown water from the HW tap in the kitchen? If so then it could be from the large white iron pipe if that is feeding your HW. Turn off the gate valve and see what HW taps stop. If the kitchen still runs then leave it running and touch a largish screwdriver to that white pipe and the handle end to your ear and see if you can hear the water flowing down through it.

 

[DP]

Jack, I WOULD fit the pump on the flow pipe ( in fact lots of manufacturers show configurations with pump in the flow pipe)
With pump on the flow, less chance of air ingress as system is at positive pressure

If the system has been installed correctly, there should be no discharge from the vent pipe

 

[Johntheo5]

The most most common configuration I think with the pump on the flow is known as a VCP system, from the boiler you have Vent, Coldfeed, Pump, with the vent and cold feed no more than 150mm apart, having said that, I know of several systems of this type where when running at high pump heads used to still draw in air when the circ pump started and stopped, these pumps were installed in the hot press, there may have been other reasons for the air ingress but I do know that in the above cases the problem was cured by combining the cold feed and vent high up adjacent to the F&E tank. My own > 50 year system was installed (from new) with the pump low down, adjacent to, and on the return to the the oil fired boiler, the system water is allways clear and some rads are > 40 years old. Long ago I think one of the reasons for installing the pump on the boiler return was because the temperature was 10 to 20C lower than the flow temp and the pump seals wern't as good as todays, most circ pumps have a max operating temp of 110C now.
My combined F&E is shown, below.

I don't know if the pumps on system gas boilers are normally installed on the return like the Vokera Vision shown but would think they would tend to be as possibly better to pump into a gas fired boiler Hx with its fairly high pressure loss than pumping away from it?.

 

[JackK]

I figure that if the pump is on the return just before the boiler then what difference will it make if it is on the flow - just after the boiler.

I cannot understand that. It needs to travel from ground floor to loft (6M) so the pressure would have already been reduced from this push up - They also have pump speeds to tweak them - Mine is at pump setting 3 at the moment!

 

[Johntheo5]

Where does the cold water outlet from the F&E tank join the system.
Is the F&E tank clean?.
You said its filthy so must be getting pump over from the vent or back through the cold feed.

 

[Madrab]

As suggested, I would suggest that the pump can go anywhere, either on the flow or return as long as it is correct in relation to the feed and vent so it doesn't put the system under incorrect pressure and avoid pulling in air or pumping over

As far as on the flow or return specifically though, there must be a reason why manufacturers seem to put their pumps on the return just at the inlet in to their sys/combi boilers rather than on the flow out from the boiler. It may be as suggested that it's better to pump into a HEX that has high resistance/pressure loss, than sucking through/out of it (so to speak)

 

[JackK]

Where does the cold water outlet from the F&E tank join the system.
Is the F&E tank clean?.
You said its filthy so must be getting pump over from the vent or back through the cold feed.

The fandE tank has been replaced and is new - I did it a few weeks ago - The fande tank is in the loft and the cold water into the heating system is also in the loft. Under the fande tank there is water going into the one pipe steep system.

So it drains from loft all the way down to the ground floor as opposed to draining from ground floor upwards.

"

You said its filthy so must be getting pump over from the vent or back through the cold feed.

I still do not understand this - If it pumps over it will dump water into the fande tank - Not cold water storage. There should be no connection to coldwater storage tank and the indirect cylinder is fed from the cold water storage tank

 

[JackK]

As suggested, I would suggest that the pump can go anywhere, either on the flow or return as long as it is correct in relation to the feed and vent so it doesn't put the system under incorrect pressure and avoid pulling in air or pumping over

As far as on the flow or return specifically though, there must be a reason why manufacturers seem to put their pumps on the return just at the inlet in to their sys/combi boilers rather than on the flow out from the boiler. It may be as suggested that it's better to pump into a HEX that has high resistance/pressure loss, than sucking through/out of it (so to speak)

The three diagrams look the same to me - FandE in loft feeding the system - How do you tell which system you have and which pressure you have and thereby where the pump should go

 

[DP]

I figure that if the pump is on the return just before the boiler then what difference will it make if it is on the flow - just after the boiler.

I cannot understand that. It needs to travel from ground floor to loft (6M) so the pressure would have already been reduced from this push up - They also have pump speeds to tweak them - Mine is at pump setting 3 at the moment!

In your case Madrab’s middle drawing will apply if the pump is between feed connection and boiler return tapping

Where does the cold water outlet from the F&E tank join the system.
Is the F&E tank clean?.
You said its filthy so must be getting pump over from the vent or back through the cold feed.

Rabs third drawing. If the 150mm link between vent and feed scales up, pump over takes place.
I could be wrong, but I seem to remember seeing that 150mm section made up from pipe one size up, bigger even.

 

[JackK]

In your case Madrab’s middle drawing will apply if the pump is between feed connection and boiler return tapping



Rabs third drawing. If the 150mm link between vent and feed scales up, pump over takes place.
I could be wrong, but I seem to remember seeing that 150mm section made up from pipe one size up, bigger even.

The third pic shown (which is desribale) would mean the pump is always on the return of the boiler Yet most pumps are on the flow and therefore pic 1

What am i missing

 

[DP]

The third pic shown (which is desribale) would mean the pump is always on the return of the boiler Yet most pumps are on the flow and therefore pic 1

What am i missing

Visualise the pump pressure differential
At the front the pressure will be positive. At the rear the pump will have negative pressure.
It follows the vent will be at positive pressure and if the feed/ expansion is at the rear of the pump, it will be at negative ( suction side)
Exaggerating the pressures for explanation of what will happen- the water level in the expansion cistern will drop and water forced out of the vent setting up unwanted circulation.

Have seen this plenty times where the vent has become a long convoluted pipe run in the loft to stop pump over. Often the pump speed is reduced in these cases to stop pumpover but still a slug of water is expelled at pump startup.

Look at Rabs drawing 3. Imagine the section between vent and feed is blocked up. The pump will lower the water level in the expansion cistern to result in vent discharge

Hope above makes sense

 

[JackK]

My FandE tank and vent is in the middle of a system - I would think most homes have this setup - My pump is on the return at the moment

How is it the case that most homes have pumps on flow and therefore option 1