Central heating problem, pics...how does this system work ?

[Mangizmo]

Hi
First post here have a problem with this system, I cant actually work out how it works as I have only had experience of Combi boilers.

My problem is as follows, hot water all ok, the radiators stayed hot even with the thermostat (a basic Honeywell in the living room) set to 0

I disconnected the thermostat and this has resulted in the downstairs rads stone cold but the upstairs rads are still warm permanently!!, I have another stat on order but surely with no stat connected there should be no central heating at all right ?

I attach 2 photos, there is a Potterton boiler downstairs, a hot water tank and expansion tank upstairs along with a honeywell timer, and valves etc as in the pic, I cant figure out what does what
Any help gratefully reciecved

See images here
//www.diynot.com/network/user_album_update.php?album_id=20402

 

[Armo74]

Sounds like a motorised valve problem.
Can't view your pictures.

 

[picasso]

Makes life a bit easier if we can see your photos

View media item 76187
View media item 76188

I would think the three port valve head wants changing.

 

[Gasguru]

Someones added an unvented cylinder and instead of keeping the wiring and controls really simple by ripping out the 3 port valve they've kept it.

This system may never have worked properly since the cylinder addition since the wiring is much more complicated.

I would ditch the 3 port valve and fit another 2 port to the heating system....wiring is then dead simple. And it's very easy to diagnose faults on.

 

[Mangizmo]

Have I got this right.....water heated from potterton boiler pumped around coil in bottom of heatrae sadia megaflow unvented cylinder, the central heating system draws water via a motorised valve which circulates around the rads and back to the megaflow, if the valve doesn't close off properly then hot water reaches the rads at all times hence the rads never go cold right ?

 

[Mangizmo]

I take it that the 3 port motorised valve is the two silver aluminium boxes at the bottom of the photograph ?

 

[Mangizmo]

Someones added an unvented cylinder and instead of keeping the wiring and controls really simple by ripping out the 3 port valve they've kept it.

This system may never have worked properly since the cylinder addition since the wiring is much more complicated.

I would ditch the 3 port valve and fit another 2 port to the heating system....wiring is then dead simple. And it's very easy to diagnose faults on.

OK its making some sense now , why have I got 2 valves? I can see the point of the 3 way but the additional 2 way, whats that for, what can I do away with ?

 

[picasso]

You can check to see if the wiring has been done properly here

http://www.google.co.uk/url?sa=t&rc...Uau04a0y0QA9PzQ&bvm=bv.65058239,d.ZWU&cad=rja



if it has worked properly in the past it may just be a faulty 3 port valve head and no you cant get rid of the two port valve, you could convert it to an s plan but I would see if a new valve head sorts out your problem first.

 

[Steelmasons]

Possibly the two port motor (brown core) has been wired in series with overheat stat with end switch parked safely within wireing centre (orange/grey) , this would allow the 3 port to function as it did before two port was added , perfectly within order with regards to regulations (overheat stat activates and closes two port).

 

[Mangizmo]

You can check to see if the wiring has been done properly here

http://www.google.co.uk/url?sa=t&rc...Uau04a0y0QA9PzQ&bvm=bv.65058239,d.ZWU&cad=rja



if it has worked properly in the past it may just be a faulty 3 port valve head and no you cant get rid of the two port valve, you could convert it to an s plan but I would see if a new valve head sorts out your problem first.

Yes has worked ok before, the 3 port head is a "plumb Centre" branded EHE0200157, the 2 port is a Honywell V4043H1056, which do you think is most likely faulty from the symptoms ?

 

[D_Hailsham]

Have I got this right

No.

Hot water from the boiler goes through the pump (red thing on the left) and into the bottom of the mid-position valve (grey box on the left). It can then go right to cylinder via 2 port valve (silver box) or left to the radiators, or to both at the same time.

The 2-port valve is there as a safety device when a mid-position valve is used.

If the mid position valve is replaced by a 2-port, the pipe from the pump would connect to a Tee joint; right exit to the existing HW 2-port, left exit to the new CH 2-port.

 

[Mangizmo]

Have I got this right

No.

Hot water from the boiler goes through the pump (red thing on the left) and into the bottom of the mid-position valve (grey box on the left). It can then go right to cylinder via 2 port valve (silver box) or left to the radiators, or to both at the same time.

The 2-port valve is there as a safety device when a mid-position valve is used.

If the mid position valve is replaced by a 2-port, the pipe from the pump would connect to a Tee joint; right exit to the existing HW 2-port, left exit to the new CH 2-port.

Great that's very helpful thanks, I will go for the 3 port valve head then and see if that fixes it as others have suggested, I can see that could cause the symptoms I have, I could as you say replace the 3 port for another 2 port, but it would be quicker and easier for me to get an identical 3 port valve head I think ?....thanks again

 

[D_Hailsham]

I will go for the 3 port valve head then and see if that fixes it as others have suggested, I can see that could cause the symptoms I have.

You described the symptoms as follows:

hot water all ok, the radiators stayed hot even with the thermostat (a basic Honeywell in the living room) set to 0

So either the valve is sticking or the stat is faulty.

I disconnected the thermostat and this has resulted in the downstairs rads stone cold

So the valve is not sticking; the stat is holding the valve open.

However:

but the upstairs rads are still warm permanently

Either the valve is letting some flow to the CH or the return from the HW cylinder has not been connected correctly to the return from CH back to the boiler, Causing what's known as reverse circulation.

You can easily check this by checking which rad pipe is hotter when the rad is heated normally, and when it is heating when it shouldn't. If it's the same pipe you don't have reverse circulation; but if the hotter pipe swaps over you do have reverse circulation.

 

[Mangizmo]

Hi guys, it is definitely the 3 port valve that is faulty, sticking open, so I have bought another to fit and need to drain the system, can anybody give me a step by step looking at the photos and advise me on how to drain and retop this system ?, I have installed and filled/drained a combi system in the past so I get the general idea

Thanks