central heating only comes on with h water, stumped engineer

[Mikefromlondon]

I am quite happy to lead op to identify his problem, you have to remember op does not seem familiar with the heating systems, somewhat like me as I am not a professional plumber, but I have gone over many installations so have acquired quite a lot of skills in this field, so to get to the bottom of this problem, what op will need to do is switch off all his system until it is cold, so all pipes are cold to touch, then he gets someone to put the Hot water (HW) on, then checks by touch each of the three pipes on his diverter valve, which of these 3 pipes starts to get hot first, he will have to be quick as the whole valve will become heated soon and he won't know through which pipe did the hot water enter first, so if I were him, i would hold the 3 pipes about a foot away from the diverter valve, so that I could feel the heat in any one of the 3 pipes first.

By logic, there will only be one pipe that will bring the hot water to the diverter valve so this will be the pipe that gets hot first.

So once he has determined which of the 3 pipes to his diveretr valve became hot or warm to touch, that is his flow pipe that should be connected to the divereter valve's middle port or the inlet port.

Then it is easy to determine the other two, since in one direction it should feed the HW cylinder and in the other direction it should lead to the CH Circuit.

So I hope you are happy with this now. And I am willing to visit if necessary FOC to help op if he lives near London.

 

[doitall]

No Mike you're loosing the plot

If the flow and return are crossed, then port AB will get hot first as one would expect.

Read my last post, and study the before and after sketch I did on page 13.

 

[Mikefromlondon]

No Mike you're loosing the plot

If the flow and return are crossed, then port AB will get hot first as one would expect.

Read my last post, and study the before and after sketch I did on page 13.

May be, you could be right, won't say you are wrong at this stage, as none of us are able to see this installation for ourselves, but what i have posted in diagrams was the exact thought I had in my mind, though when you said that you were working on a picture and were going to post it, I thought that was so good of you, and thanks you did that, you understood it your way, the idea in my head was similar but as it turned out when you posted your picture, it was not far off my thoughts, so I accepted it rather than saying no thats not what i had in my mind, so i studied your diagrame and I could see your logic behind it, and I can hinestly say it also makes a bgreat deal of sense, but we cannot be 100% certain so both yours and mine seem to adhere to the symptoms of the problem and the logic of it, either way, whichever is the situation, op has two senarios, which one is actually there we don't know, I went back to read some of the posts and saw some pictures of op's cupboard where his cylinder is installed, I could see his pump motor but I couldn't see his diverter valve unless I missed it some how, as looking at that diverter valve if its mid port was connected to the pump, it would indicate that indeed you are right, the flow and the return pipes may have got mixed up., but if not then my theory is correct. Still I pat you on you back for your valuable input and encouragement, as we help one another with suggestions and this provokes better thinking and understanding.

 

[Mikefromlondon]

No Mike you're loosing the plot

If the flow and return are crossed, then port AB will get hot first as one would expect.

Read my last post, and study the before and after sketch I did on page 13.

Indeed, I don't disagree there, that would be the case, with your senario, similarly with my senario, it would be port BC, only a practical test using the same touch/feel heat method that you and I suggested would determine this. ie, which of the 3 pipes first gets hot leading into the diverter valve.

hats off to you as well.

 

[UpgradeME]

I went back to read some of the posts and saw some pictures of op's cupboard where his cylinder is installed, I could see his pump motor but I couldn't see his diverter valve unless I missed it some how, as looking at that diverter valve if its mid port was connected to the pump, it would indicate that indeed you are right, the flow and the return pipes may have got mixed up.,

Untitled

• bonkersbill
• 25 Feb 2012
• 1

 

[Mikefromlondon]

thank you upgradme, that picture clarifies that. pump does indeed feed the port A, so we take it from there, I hope op would be able to fix his problem now finally.

Mind you at first if you don't look more carefully, the angle of the picture taken can easily mislead you with that other pipe sticking from port B upwards in front of the pump. But yes if you exapand the picture you can't miss the fact that the pump is conncetd to port A

My respect to doitall and others.

But between us all we have somehow got to the bottom of op's problem.
happy ending chaps!

 

[doitall]

The pump is feeding port AB Mike, as it should.

The theory is the flow and return got crossed over during the alterations, so the MV and pump are actually on the return pipe and not the flow.

 

[Mikefromlondon]

The pump is feeding port AB Mike, as it should.

The theory is the flow and return got crossed over during the alterations, so the MV and pump are actually on the return pipe and not the flow.

Got you now mate, thanks again, problem was my theory was based purely on logic of the symptoms without looking at that picture, I obviously went back to some of the earlier threads to see where that other guy 4expaws had come up with this first, so as I was going through pages after after pages of posts, I saw those pictures op posted, and I failed to notice the diverter valve, I must admit it I was in a hurry to see 4expaws post so did not give a through look at those pictures, so i missed it out, if I had seen those pictures clearly and seen the diverter valve was connected correctly, I would not have made those pictures for posting here, but if that is what i had in my mind that provoked your thoughts, you did it, well done. and thanks again. we all win. You win more! Glass to you full of beer! (lol)

 

[Mikefromlondon]

Here we are Doitall, I simply put the flow and return by just crossing over, which leaves everything you drew as was only moved the two pipes to show op whats happened, this way is less confusing I hope as i haven't changed the pipes at the boiler end, but all this could be done in the HW Cylinder cupboard quite easily. kind regards

Op, you will need to remove the pipe from the pump and connect it to the cylinder and the one from the cylinder to the pump, making sure the pipe that connects to the upper section of the cylinder is from the diverter valve as hot water surfaces towards the top so hot water from the pump and through port B of the diverter valve should be connected to the upper connection and the bottom is your return.

 

[Mikefromlondon]

I have another thought provoking idea!














































with this 14 page script, we can turn to hollywood for comedy movie!
If I can, can i nominate UpgradeME for the main charachter

 

[UpgradeME]

Op, you will need to remove the pipe from the pump and connect it to the.....

OP, before making any changes to pipework, I would like to point out this is still only a theory as nothing yet has been proven. I would therefore suggest you follow DIA's earlier post (reposted below for clarity) which only requires you to disable the pump.

Actually proving the theory is very simply.

Remember I said the primary pipes would have been gravity, so all you need to do is, set the MV in the mid position, turn the boiler to low, and disable the pump.

Hang around the cylinder and see which pipe gets hot first.

The two pipes you want to be checking are the pipe feeding the top of the pump (as far back as you can reach) and port AB on the 3pv. Whichever gets hot first is the 'feed' (it should be the pump but if the theory is proved correct will be port AB).

 

[doitall]

The two pipes that need checking are the one feeding the pump, and the one exiting the bottom of the cylinder.

They will be the existing primary flow and return.

I think you'll find the pipe in the bottom of the cylinder will get hot first, if the pump is disabled.

Unfortunately, it will mean virtually re-piping the cylinder to swap them over.

 

[UpgradeME]

The two pipes that need checking are the one feeding the pump, and the one exiting the bottom of the cylinder.

I suggested port AB in case there was an easier flow through the radiator circuit pipework and both the cylinder and radiators feed into port AB.

If the flow/return ARE correct (i.e. pump gets hot first), the CH return could still have been plumbed into the flow pipe during alterations. My earlier test using a thermometer will prove / discount that theory.

 

[doitall]

I think if any test is inconclusive the OP will need to expose the pipes and visually check the pipes. In fact now he has something to check it could be the best plan.

If the theory is proved, there may be a way to swap them over in the box to save having to re-pipe the cylinder.

There could still be an old MV hiding in the boxing that open/shuts with the hws program

 

[bonkersbill]

I dont want to spoil anything but the pipes into the boiler dont look like your drawings [GALLERY=media, 43372][/GALLERY]
This is what i can see, i'm not 100% on whether anything tees into the 28mm pipes further up the conduit but i would say not

I am able to blow through the old 3pv easily when opened in all 3 positions, 1st port A then B then Both and i can see all ports are clear.

i have been to 4 plumbers merchants today looking for clip on temp gauges and none had one in, if i still need them i will buy online.


i cant make out which pipe is which from boiler to the under floor by looking, this will need testing using temp