Converting close coupled to combined feed & vent

[nairb999]

I have received a lot of good ideas/advice and would like to summarise my options. I still think I have 2 problems - firstly a 10 year problem from when the system was fitted ie had to regularly bleed the radiators. This was a new house and so the house builder put some inhibitor in the system which reduced the amount of air but not completely. 5 years ago the heat exchanger failed and then 4 months ago the pump was replaced - the old pump worked perfectly fine but kept tripping out the mains RCD. After replacing the pump that is when the sizzling water noises started and only present when the boiler is at full temperature ( stat set at about 2.5 ) and lasts for up to a minute - although some of that time the boiler is off but I presume the hot water is still on its way to the pump.

Although not everyone is convinced combined feed & vent will work - I feel I have to give it a go. My next door neighbour's house is identical to mine with same heating system except his feed pipe runs 50 mm parallel to the vent pipe. This then t's into the short horizontal pipe above the pump before after another 70 mm it connects to the pump pipe inlet with an elbow. He does not have any air problems

Agile's post looks the preferred option and after digging through the boiler manual they actually show this as a typical layout

Converting to a combined feed and vent will normally solve any problems.

You could do this within your room will be OK but do use 15 mm for the feed.

Tony

Yesterday though I thought I would have ago at implementing a version of combined feed & vent option offered by twgas

cold feed needs to be in 22mm from tank to system and do away with open vent. easiest way is to cap 15mm and drill and fit a new 22mm tank connector. enlarging a hole in a tank is more difficult than fitting a new one.

I have temporarily removed the vent pipe by disconnecting compression coupling above t and capping it several inches above - no vent at this time and I did not change the 15mm feed pipe at this stage. The method in my madness was it was simple to implement just emptied the tank and ran off a pint or two of water before installing the temporary cap - 10 min job. Bled the system eventually - I now understand Gasguru post of difficulty of bleeding the system in this configuration. On start up the pump is fairly noisy for a couple of seconds. Could this be due to the air pocket that could exist in the cap.

Sizzling water noises again appeared after system got up to heat and I ran the system for 6 hours. This morning bled the radiators - 2 emiited a little air upstairs and one downstairs. The amount of air released was considerably less than previous days so I am thinking that going to combined set up would work.

I still have the sizzling water noises - very noticable around the pump and the pipework in the airing cupboard. The noisee does not appear to be in the pipes around the boiler.

So I am now thinking that problem could be resolved by cowley's

Add fernox/sentinal or other as you prefer to system as per instructions/quantities etc and circulate through boiler,primary flow & returns hot water circuit rather than heating circuit not the best time of year to do this, or power flush through this circuit.

Comments would be greatly appreciated

 

[Agile]

I cannot give advice to someone who gives credance to Dr Drivel.

Tony

 

[nairb999]

Ha Ha !!!

I suppose I dont need to say "I told you so" ???

I really always wonder why these DIYers always think they know better than the professionals!

If you left the 15 mm tube to the F&E tank in place then you may have left an unsafe situation!

Tony

Tony - I am indebted to all the advice I have recieved. I will convert to your suggested configuration immediately. On another post you recommend connecting the feed 100mm below the expansion tank so I can do this but it will mean making the connection in the loft. You originally suggested I could make the connection in the airing cupboard but this would mean 300mm below the tank.

What do you think about another suggestion to chemical clean again but concentrate on heating circuit

 

[Agile]

Professional advice removed!

Tony

 

[nairb999]

The ideal is 100 mm below the base of the F&E tank but as I said doing it in your room will still be OK even if its 300 mm below.

Do keep the F&E pipe in 15 mm though.

I do hope it will work for you! My reputation depends on it!

Tony

Tony - thanks for prompt response. It is just as easy for me to make the connection in the loft. So final 2 questions - loft or airing cupboard and if the sizzling noise remains would you recommend chemical cleaning.

Once again the advice given by you and your other professional colleagues is most appreciated

If you are interested I could post again when I have completed the work

 

[cowley]

Is he suggesting linking the vent pipe into the feed pipe[/quote]

NO!

I am suggesting that the feed pipe ( in 15 mm ) is connected into the vent pipe!!!

There is a subtle difference!

The vent pipe remains in an unobstructed near vertical 22 mm pipe. The feed pipe tees into this 22 mm about 100 mm below the base of the F&E tank.

Tony[/quote]

Tony is right to point out my mistake, I misread the post, but i hope he isn't implying that i,m a DIYer.

 

[Doctor Drivel]

My system is closely couple as indicated in the following photos

http://i3.photobucket.com/albums/y66/cragga_lfc/dad/CentralHeating004.jpg

This picture is showing left riser from Boiler - top left going to vent - top right cold feed and bottom right into pump ( arrow on the pump pointing down

http://i3.photobucket.com/albums/y66/cragga_lfc/dad/CentralHeating005.jpg

This picture is showing pipes going to the loft where the feed/expansion tank is directly above

I saw a lot of well meaning advice which is just plain wrong.

You need to re-pipe.

• 
  [*]From the boiler have the flow rising,
  [*]then a bend to the right,
  [*]a length of horizontal pipe then a bend down to the pump.
  [*]Keep the horizontal part as low as possible - [*]you can get it lower than that.
  [*]On the horizontal section have two tees, right next to each other.
  [*]The left tee to the open vent
  [*]The right to the cold feed.
  [*]The bends are important to give ease of flow from the boiler to the pump.
  [*]Also get rid of those two elbows on the flow, which restrict flow.
  [*]Fit a Magnaclean or Boiler Buddy filter on the return to the boiler with a full-bore 1/4 turn valve either side - the valves they supply are crap.

Sorted.

The prime flow must be from the boiler to the pump, with bends, and no elbows. At the mo' the pump is acting primarily on the cold feed of the F&E tank with the flow from the boiler teed in - wrong. The vent and cold feed must be teed into the flow line, not being the main pull of the pump.

 

[DP]

I have only read first one and a half pages of this post and am surprised no one has noticed the pump is fitted on the FEED pipe to the boiler. No wonder there is pump over / or suction taking place. It is elementary knowledge that the pump should never be fitted on the feed or the vent pipe.

If you want to correct the problem (it will be very easy in your case as feed and vent pipes are conveniently run), locate the flow from the boiler and tee the vent into this pipe. Within 150mm, beyond the vent connection, connect the feed pipe such that the feed joins the flow pipe from below, i.e. feed drops past the flow pipe and then doubles on itself to connect to the flow pipe. Now fit the pump to the flow. Fit a bypass if S plan fitted

 

[cowley]

I have only read first one and a half pages of this post and am surprised no one has noticed the pump is fitted on the FEED pipe to the boiler. No wonder there is pump over / or suction taking place. It is elementary knowledge that the pump should never be fitted on the feed or the vent pipe.

Your talking rubbish, the vent is a part of the flow pipe & the feed & expansion pipe is connected to suction side of the pump as it should be in a H system layout which this is also no pumping over mentioned in this post.
The pump is fitted in the flow pipe where do you fit yours?.

 

[nairb999]

I have only read first one and a half pages of this post and am surprised no one has noticed the pump is fitted on the FEED pipe to the boiler. No wonder there is pump over / or suction taking place. It is elementary knowledge that the pump should never be fitted on the feed or the vent pipe.

Your talking rubbish, the vent is a part of the flow pipe & the feed & expansion pipe is connected to suction side of the pump as it should be in a H system layout which this is also no pumping over mentioned in this post.
The pump is fitted in the flow pipe where do you fit yours?.

Cowley - Is Doctor Drivel on the same plane as you. You were not happy with combined feed and vent arrangemen

 

[cowley]

I was not happy with doing away with open vent, not combined system what i said about that was i didn't agree that altering the pipework to this would cure your particular problem.
I take it that you are insulting my intelligence and don't want advice.

 

[nairb999]

You need to re-pipe.

[*]From the boiler have the flow rising,
[*]then a bend to the right,
[*]a length of horizontal pipe then a bend down to the pump.
[*]Keep the horizontal part as low as possible - [*]you can get it lower than that.
[*]On the horizontal section have two tees, right next to each other.
[*]The left tee to the open vent
[*]The right to the cold feed.
[*]The bends are important to give ease of flow from the boiler to the pump.
[*]Also get rid of those two elbows on the flow, which restrict flow.
[*]Fit a Magnaclean or Boiler Buddy filter on the return to the boiler with a full-bore 1/4 turn valve either side - the valves they supply are rubbish.

Sorted.

The prime flow must be from the boiler to the pump, with bends, and no elbows. At the mo' the pump is acting primarily on the cold feed of the F&E tank with the flow from the boiler teed in - wrong. The vent and cold feed must be teed into the flow line, not being the main pull of the pump.

Doctor Drivel - Have I interpreted your advice correctly. Would the cold feed now be 15mm? If so , this is exactly the same as my next door neighbour who has the same boiler and arragements as me other than feed

 

[nairb999]

I was not happy with doing away with open vent, not combined system what i said about that was i didn't agree that altering the pipework to this would cure your particular problem.
I take it that you are insulting my intelligence and don't want advice.

Cowley - I really appreciate your professional help - along with all the other advice I am getting from professionals. Please bear with me - I am a simple DIYer wishing to get it right. I am going to take your advice and clean the heating circuit as you advised but I think I will still have the problem of air getting into the system hence my wishing to change the piping arrangement.

 

[cowley]

In your drawing if the cold feed pipe was inline with the pump it would be exactly what you already have apart from the horizontal part closer to the pump a standard H system.

 

[DP]

THE OP wrote >>>This test revealed water being sucked up the jar for 1 second and then falling back inot the jar followed by a number of bubbles then the level stayed steady<<<<

Certainly not what should happen if pump was fitted to the flow pipe.

A pump (or for that matter any valve or fixture) should never be fitted to the flow pipe or the F+E pipe where safe discharge of pressure will be impeded. If you are doing this, then I suggest you get hold of relevant BS publication or talk to the boiler makers whose boiler you are fitting in this manner.

Look at the drawing again. Also look at the posted pictures. Cowley, according to your last post, you are implying a vent pipe would be fitted to base of the boiler (feed connection) and F+E to top connection on the heat exchanger (which surprise surprise was a 15mm pipe now replaced with 22mm- see body of the thread)