Central Heating Pipework Help!

[Mazzy]

Hi There

I have had ongoing issues with my central heating since moving in 18 months ago.
The main issue was the ground floor rads being luke warm at best - particularly when the HW was on. Balancing didn't really help much!
Since Christmas we have been having boiler lock out issues that are 'ignition faults' and so with the numerous engineers that have tried to help and provide us with quotes - we keep getting different answers and suggestions to our problems. We are now not knowing what to do, other than try to understand out system and understand it for ourselves.

I want to get to the route of the cause and not just fix the symptoms - I think with some research I have done (and an engineer who is willing to try and help us through this), that it may come down to the pipework design up in our airing cupboard.

My notes below give a brief description of symptoms and what has been suggested by engineers and how to fix it.
We believe our system is fairly old and has lots of isolation valve scattered around so we are a bit nervous about doing anything too harsh to it.

Symptoms
A. Boiler is sporadically/regularly locking out
B. When pump turns on - vent sucks in air
C. When pump turns off vent spits small amount of water
D. When CH or HW on the cold feed gets very hot and
header tank water turns warm
E. 2 Rads on ground floor never get as hot as others

Obvious Issues
1. Vent and Cold feed too far apart
2. Vent pipe not 450mm above water line
3. Poor pipework design after pump.
4. No Balancing valve on HW tank

Other possible issues
1. Sludge in system - (Thermal image
suggests otherwise) Have tried Fernox F5
2. Cold Feed Tee blocked
3. Pump not large enough
4. Unbalanced system - have tried this
previous to Fernox F5 without much success.

I have drawn a diagram of the pipework - can anyone see anything glaringly obvious which could be causing lock outs with the boiler or flow issues to the ground floor?
Any help would be greatfully received.

Marrianne

 

[D_Hailsham]

Obvious Issues
1. Vent and Cold feed too far apart
2. Vent pipe not 450mm above water line
3. Poor pipework design after pump.
4. No Balancing valve on HW tank

1. Agreed. They should be not more than 150mm apart. Move the vent pipe connection nearer the feed, so it is teed of the horizontal pipe.
2. It's the top of the bend which needs to be 450mm above water line.
3. One of the arrows is pointing in the wrong direction! I have corrected it in red. The "isolation valve" is a manual bypass. This is not needed as you have a mid-position motorized valve, so it should be closed.
   
4. This would be a useful addition.

 

[Mazzy]

Thanks for your reply.
Do you think your suggested changes would fix the issues with the header tank?

I am still wondering if there is anything else stopping the flow getting down to the ground floor. Do you think a balancing valve on the HW cylinder and making sure the bypass is shut would make much of a difference?

Also the way the pump is plumbed to the system seems a bit odd to me. Having such a short flow pipe after the pump logically to me must be slowing the flow down - what do you think? Could it benefit from reconfiguration?
Attached a couple more diagrams of possible re configurations...

 

[D_Hailsham]

Do you think your suggested changes would fix the issues with the header tank?

It will stop the over-pumping (water coming out of the vent pipe) provided the pump is set correctly.

Do you think a balancing valve on the HW cylinder and making sure the bypass is shut would make much of a difference?

Yes. As currently configured the bypass is a a direct short cut back to the boiler, so water will prefer to go that way, not through the rads. When HW and CH are both on, the cylinder will also act as a short cut, reducing the flow through the rads/

Also the way the pump is plumbed to the syste m seems a bit odd to me. Having such a short flow pipe after the pump logically to me must be slowing the flow down - what do you think? Could it benefit from reconfiguration?

That's not important - the T junction below the valve just provided a little bit of extra resistance to flow, which the pump can easily handle. If you want to change it, your diagram 3 is the better way. Don't forget that the feed from the pump must go to the centre connection (marked AB on valve); radiator circuit connects to connection A and cylinder to connection B.

What is the distance between the pump and the bottom of the header tank? If needs to be at least one metre.

What is important, and I should have picked it up earlier, is the connection of the return from upstairs rads, which is wrong. The last connection, before the boiler must always be the return from the cylinder. If it is not, as in your original diagram, you can get reverse circulation, i.e water travelling backwards along the return pipe, making the rads heat up when they should be cold. This diagram shows, in green, where the return should be connected.

When you have made all the changes, the system will need balancing.

 

[Steelmasons]

What is important, and I should have picked it up earlier, is the connection of the return from upstairs rads, which is wrong. The last connection, before the boiler must always be the return from the cylinder. If it is not, as in your original diagram, you can get reverse circulation, i.e water travelling backwards along the return pipe, making the rads heat up when they should be cold. This diagram shows, in green, where the return should be connected..

The cylinder return can be the first/2nd/3rd/4th connection back to boiler as long as all radiator returns are connected before the cylinder return enters manifold .....we could have 6 heating zones with the cylinder return tee being the furthest from boiler.
Reverse return will only cause an issue if heating returns straddle the cylinder return where it connects into common return manifold.

 

[Dan Robinson]

 

[Mazzy]

Thanks again for your responses.
The bottom of the header tank is about 1.5 -2 meters away from the pump. It's not directly above but slightly off to the right as it has all been wedged into a tiny space in the eaves of the second floor and the header runs up the roof line into the tiny roof space. It's pretty hideous on space which is what is putting off most engineers from doing anything to it.

In my original drawing the return seems to do some sort of loop at the top of the system is this normal? I am also not sure of which direction it currently flows around the loop - I only guessed that they were both going south since they are returning pipes to the boiler, therefore it could be flowing anti clockwise meaning the rad returns are in the right place?

I can upload photos if you need - but it is quite hard to photograph due to the space constraints!


Steelmasons - I don't really understand what a manifold is and I don't have heating zones (if that is what you mean) the whole house (3 floors) is on or not at all. The top 2 floors get baking hot even when DIY balanced and the ground floor still takes all evening to get comfortable. It's weird as it only affects 2 out of 4 rads, typically the 2 that are in the main living space rather than the kitchen!

I have had a guy round to do a thermal image on the rads as other guys have suggested a magnacleanse powerflush but he doesn't think they are sludged up - he thinks it is a flow issue. The 2 rads in question where white at the top, red in the middle and yellow at the very bottom. No pyramids of sludge in the middle.
When the heating and HW are on together, one of the rads occasionally doesn't get any heat to it at all. The flow pipe is burning hot but it just doesn't enter the rad. We are planning on draining the system next weekend and hope to take this rad off the wall and flush it through with a hosepipe.

My husband and I have become completely obsessed with the system trying to work out what is wrong for the last 18 months.
We are sick to death of it now, we have asked people to come and quote for cleans (because of the cooler rads and the boiler locking out when it first comes on) and a balancing valve on the cylinder and they all end up looking at the whole system and diagnosing something different.

Thanks again guys

 

[D_Hailsham]

The cylinder return can be the first/2nd/3rd/4th connection back to boiler as long as all radiator returns are connected before the cylinder return enters manifold .....we could have 6 heating zones with the cylinder return tee being the furthest from boiler.

You seem to be talking about commercial installations with separate flow and return headers (manifold?)
If rad returns have to be connected before cylinder return enters manifold how can the cylinder return tee be furthest from boiler? It must be the nearest.

A pic or diagram to illustrate your assertion would help.

Reverse return will only cause an issue if heating returns straddle the cylinder return where it connects into common return manifold.

And that's exactly what is shown in the OP's original diagram. (Though, reading her latest post, that is now questionable.)

 

[Mazzy]

The guy who thermal imaged the rads also measured the temp difference between the flow and return on the boiler and it was only 10 degrees. Does that help to determine what the pipes are doing?

 

[D_Hailsham]

Do you know what the actual temperature were? If so the higher is the flow, and the lower the return.

 

[Mazzy]

I can't remember exactly. Something like 60 and 70. The left hand should be the flow and the right the return. I have ordered myself a radiator balancing thermometer so can check it myself soon.
I am almost convinced that the bypass is open and returning the water before it has a chance to get round the system.
It is very frustrating though as the top floor rads are off and half the middle floor ones are off or low to try and get the flow pushed down stairs.
I am beginning to wonder if we have some blocked elbows on the ground floor or the lockshield on the worst rad is blocked. Very tempted to change it.

I should also mention, going back to the pipework configuration, that some of the tees I have tested with a magnet for build up. One or two of them do start to pull the magnet - but not enough to hold it without my support.
Feeling like i need to rip it out and start again! Such a lot of info to get my head around.

 

[Ron_3]

Mazzy, did you get to the bottom of this? I am having similar problems and my system is laid out very close to yours. I have done a chemical clean, drained and flushed a few times, bled and balanced, and I still cannot get 1 or 2 radiators downstairs to kick in. The only differences from your system is that my hot water tank is on a separate valve (although the water enters from and returns to the same flow pipe direct from the pump), the cold flow and vent are closer together, and the vent pipe is only slightly higher. Also, I think my bathroom radiators completely bypass the valves as they get hot when the hot water is on but heating is off. Anyway, interested to know if you found a solution before completely re-plumbing the whole system.

 

[CBW]

Ron, you’ve just hi-jacked a near on 4 year old thread, which is against forum rules, and you issue seems different, start a new thread so it’s not as confusing.