CH problem

[cstokes]

I have quite a serious problem with my central heating at the moment. The system has never been efficient, I've never managed to get all of the radiators hot. A few of the radiator valves were very old so I changed them, plus I needed to change the pump. Unfortunately now the upstairs radiators only heat up near the in pipe, leaving the return pipe and the rest of the radiator quite cool; the downstairs radiators are cold (although I know this would be because I havent balanced them since draining the system). I'm completely confused especially as when I turn the heating off the two upstairs radiators heat up completely. There is also a glugging sound from the radiators when they go off.

Any help would be appreciated.

Thanks in advance

 

[kevplumb]

the system is

 

[cstokes]

Its an open-vented gravity fed system.

 

[kevplumb]

is the system full of water
is the system vented
try opening the locksheilds fully
get some cleanser in quick

 

[cstokes]

"is the system full of water"

Yes, it was drained completely today and refilled until water escaped from all of the radiator bleed valves which I take as meaning the system is full of water.

"is the system vented"

Obviously I'm sounding really amateurish but what does this actually mean!!


"try opening the locksheilds fully"

I've attempted to islolate a single radiator by fully opening the lockshield but the rad only heats up on the in flow pipe side of it and goes quite cold on the other (where the lockshield is). The radiator fully heats up once the pump is turned off.


"get some cleanser in quick"

I took off two of the radiators and flushed them, yes, getting rid of some sludge in the process. The water that I drained from the system today was clear.

All of my lockshield valves are on the return pipe side of the radiators. I'm wondering if there is a blockage in the return pipe as the pump (which is next to the boiler on the return pipe) does not seem to pull the water out of the lockshield side.

 

[kevplumb]

take the rads off
open the valves (bucket may be handy )
see how much flow you get out of both

 

[cstokes]

thanks very much for all your replies kevplumb but could you just explain in a little more detail that last post of yours as all I have visions of is having to put a new ceiling in my living room

 

[kevplumb]

take the offending rad/s off then open the valves into a bucket
and see what sort of flow you get should be reasonable if its slow the pipework might be partially blocked
you might be lucky and shift it (dont bet on it )

 

[MANDATE]

You'd be better equipped with a hose connected to the valve when you run water off. I use clear plastic tubing between two 1/2 in tap connectors each soldered to 3 in of 15mm pipe. It can be used to run water off or fitted in place of the radiator then you can see what is happening.

 

[kevplumb]

good point but if old valves will be 3/4""

 

[felix]

Since it's never worked properly let's not overlook a simple possibility. Do you have a bypass? This is a simple piece of pipe that allows water to circulate through the pump and boiler only, bypassing the rest of the circuit. There will be a valve in it and this should be almost shut. If it's wide open the water will take the easy route and leave you with cold radiators. The boiler will cycle on and off on its own thermostat, spending more time off than on because the water is coming back almost as hot as it went out.

 

[cstokes]

I wish it was that simple but I dont have a bypass. The out pipe taking the fresh hot water seems to do a good job, its just when it gets in the radiator it doesnt really like leaving via the return pipe even when all radiators are closed and just the closest one to the boiler is fully open This is what is leading me to thinking there is a blockage in the return pipe

Thanks for all your replies.

 

[felix]

The blockage, if that's what you have, doesn't have to be in the return pipe. It could be anywhere round the circuit. Since hot water is getting to the radiators you must have some minimal flow but it's so feeble that only cold water emerges from the other side.

Now here's another puzzle. You said the radiator fully heats up once the pump is turned off. Did you really mean that? If it's true then you have no blockage because gravity alone is enough to push water through the radiator. I have no immediate explanation as to how the pump can fail where gravity succeeds. There are more questions than answers at the moment.

Here's another thought. Do you have a three port valve? These rest in the HW only position and must drive to open a path from boiler to radiators. They generally have a manual over-ride lever on the side. If you think the valve may be stuck in HW only you can try this.

 

[cstokes]

Yes, when I turn the central heating off there is a large gurgling sound and the radiators heat up, as if some sort of pressure is being relieved, although that is omplete supposition on my part

I'm going to put in a restorer and hope that dislodges any blockage if thats what I have, I suppose it can only hurt my wallet.

I dont think I have a 3 port valve, if I do then its very well hidden

 

[cstokes]

Ok, I put a heating restorer into the header tank last night. I did notice the header tank was quite murky, which surprised me as I'd drained the system recently. After putting the restorer into the tank the central heating was turned on and I noticed a lot of dirty water coming out of the overflow into the header tank. When the heating went off the header tank emptied a fair amount. I assume some of this is due to the pump being on maximum but could it be made worse by a blockage in the pipework?

I'm trying to get rid of the mirky water that is coming into the header tank but I'm now wondering whether the restorer has actually gone into the pipework or is just coming back up and into the header tank!