Radiators All Hot Upstairs, All Cold Downstairs..... (but different)?

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Hello to all

I've got a problem that began to occur yesterday, but sees to be slightly different (I think) to some others that appear similar on the forum.

We have a four bedroom house. The Stelrad boiler and Grundfos pump are out in the garage. The pump sits just above the boiler. The Potterton timer and Honeywell diverter valve are both in the upstairs airing cupboard along with the hot water cylinder tank. There is a single thermostat in the downstairs hall.

From yesterday, all of the radiators downstairs have not been heating up. Indeed, as of yesterday evening, none of the radiators anywhere were heating up at all. My first step was to bleed all of the radiators.

All of the upstairs radiators (4x bedrooms and 2x bathrooms) had air in them, and this has now been expelled. None of the downstairs rads had any air in them, with water leaking out of the check valves immediately upon opening them.

I turned the heating on and fiddled with the silver lever on the bottom of the diverter valve. Eventually, and after much fiddling, I managed to get some heat appearing in the upstairs rads, and these are now getting "very warm" if not quite "boiling hot" as before.

I can see that the boiler is on and firing. It appears to be working ok. After taking hot water our of the taps, I could see that the boiler was coming on and heating water and then going off again.

The Grunfos pump by the boiler however is getting extremely hot indeed. It was scalding to the touch. The last time this happened, about two years ago, it turned out to be the Honeywell diverter valve that had packed up, and this was replaced with a brand new unit and has been working perfectly ever since. As it happens, a brand new Potterton timer was also fitted at the same time, as I had incorrectly diagnosed this as the fault. This is why I was fiddling primarily with the diverter valve last night, as it seemed to be the same thing happening over again. The diverter valve is now set back as it should be with the small silver lever set to "auto".

This morning, the rads came on, but only upstairs again. All of the rads downstairs were icy cold.

From searching other similar reports of similar problems, the advice seems to be to turn off the rads that are working and force the pressure onto the ones that aren't, and to expect the rads nearest the boiler to heat up first - this is the thing. The radiators in the hall and lounge are the nearest to the boiler, and to be fair, when the system is working properly, these are the first to heat up. However, they're just not. This is what I don't understand, but I am guessing that the pipes from the boiler/pump in the garage, actually lead upstairs and directly to the airing cupboard as the first port of call. I can see that the pipes leading away from the boiler, feed into the roof of the garage and then enter the house at about "upstairs ground level". I am guessing that the pipes feed under the floor of the 1st floor, and then pop up through the floor of the airing cupboard hitting the diverter valve first, then either entering the hot water tank or the central heating system. This leads me to conclude that the rads that should be heating up first are in fact the upstairs rads, and then reliant on a part gravity / part pump pressure to feed the hot water round the rest of the system to get round the rest of the house and, in particular, the downstairs rads?

Checking the hot water pipes coming out of the diverter valve, when the CH is on on the programmer, they're all really, really hot - both going to the hot water tank, and the other two which must be the central heating pipes. Therefore, the hot water must be making it up the system from the boiler, being pumped upto the airing cupboard to get this far into the system.

This is why I suspect the most likely candidate at the moment is some sort of air blockage or air lock? I'm continuing to bleed the rads, but there's no more air coming out of any of them at the moment... Gggggrrrrrrr

I am also concerned about the temperature of the pump, which shouldn't be getting this hot - it's clearly overworking, or stuck or broken or something - I know that it just shouldn't get this damn hot. However, I've now reached the limits of my knowledge about what to do next, or what really is the root cause of the problem actually is?

Also, normally, when you press the CH button the programmer to override its set times and bring the CH on, there is a "click", a bit of gurgling, and then a flow of water (that you can hear in / around the airing cupboard) and you can hear the flow of water. At the moment, there is nothing, so I am concerned that it might be the pump that is either kaput, or close to kaput?

Finally, I have just checked the CH expansion tank in the loft. This seems to be exactly as it should be, is 3/4's full and at the same white "limescale" line around the inside of the tank as it clearly has been for years.

I would be really, really grateful for any advice/pointers to help me diagnose and fix the problem.

Many thanks in advance for any replies.
 
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that was very long

you say the pump is very hot. Is it hotter than the pipes on either side of it? If so, it is not circulating water. The water takes away the heat resulting from the electric current passing through the motor windings.

Turn it all off, remove the large central screw in the pump, put a small screwdriver through the hole, and see if you can turn the spindle by hand (it has a slot in the end). If you can, leave the screw out, turn the power back on. Is the spindle now spinning, driven by the motor? Water may drip out, but it will not gush out.

Is the hot water cylinder surprisingly hot?
 
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that was very long

you say the pump is very hot. Is it hotter than the pipes on either side of it? If so, it is not circulating water. The water takes away the heat resulting from the electric current passing through the motor windings.

Turn it all off, remove the large central screw in the pump, put a small screwdriver through the hole, and see if you can turn the spindle by hand (it has a slot in the end). If you can, leave the screw out, turn the power back on. Is the spindle now spinning, driven by the motor? Water may drip out, but it will not gush out.

Is the hot water cylinder surprisingly hot?

Hello JohnD

Thank you very much for the prompt response - yes, but important to get as much detail in for diagnosis!

Good question - Yes, the short pipe from boiler to pump and pipe after the pump are both very cool to the touch. The pump is still extremely hot to the touch.

I undid the large screw on the front of the pump and some pretty hot water started to stream out (it was more than I was expecting - not a gush, but a definite slow flow), so I've turned everything off for now, to give it a chance to cool down a bit. Will attempt to turn the spindle when the water temp has cooled down.

I have given the pump a few "loving" whacks with a small hammer, to see if it could be freed off in case it was stuck. It didn't seem to make any difference. I will also check the 2amp fuse in the pump plug, just in case I get lucky and it turns out to be this. Probably won't be though :(

The pump is original, so some 30 years old now, so if it has finally gone, I can't be too disappointed with that.

Also - I have checked the hot water cylinder, but could only feel it through the padded jacket. The insulation felt pretty cool to the touch, so didn't seem to be overly hot - however, I can't recall ever touching it / testing it for heat before, so I would have expected it to be pretty hot all of the time filled with boiling water?

PS - I can't get any rad to get warm now. Had the CH override on for an hour or so, but no rad got hot - not even the ones upstairs that got warm this morning when it was running on auto.

Also - found that I had resistance on the water diverter valve silver override lever. Last night, I didn't. Last night, I could move it from auto to manual and it would just stay there in the manual position. This afternoon, when I did the same thing, I could feel and hear the resistance of gearing inside the silver box on the back of the diverter valve, which slowly pushed the lever back to auto by default when you let it go. Any relevance here?
 
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I concur. Next week I am changing a neighbour's pump. Totally dead, but got water and heating on upstairs. Downstairs brassic.

Quite surprised as I didn't think the boiler would function under gravity, and seing as their house is identical to how mine was before we renovated it, I know the pipework is certainly not, in theory, capable.

Good old British Gas ; told them they needed a Powerflush. Without even checking the 32 year old pump :LOL:
 
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you say the pump is very hot. Is it hotter than the pipes on either side of it? If so, it is not circulating water. The water takes away the heat resulting from the electric current passing through the motor windings.

Turn it all off, remove the large central screw in the pump, put a small screwdriver through the hole, and see if you can turn the spindle by hand (it has a slot in the end). If you can, leave the screw out, turn the power back on. Is the spindle now spinning, driven by the motor? Water may drip out, but it will not gush out.

Hello again JohnD

Discovered that there is no fuse in the pump plug.... :facepalm:

Right, allowed the pump to cool, and removed the screw. It was pretty hard to see inside it, if I am honest, as there was a gentle flow of grubby water out of it. However, I am confident that I could turn the spindle manually with a screwdriver. I think I could see what I was touching with the screwdriver turn as I was turning it, but as I say, it was dim and wet. Every time I turned the spindle manually, more water would come out of the inspection hole. The spindle would turn in both directions.

I've turned the system back on, and some of the rads upstairs are getting hot again, but not all of them. The pipe coming out of the pump is definitely much warmer to the touch than it was earlier. Once again, the pipes leading off the diverter valve are extremely hot indeed, therefore, I don't understand how the pipes from the pump are just "warm", and the pipes from the diverter valve are boiling hot?
 
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I concur. Next week I am chasing a neighbour's pump. Totally dead, but got water and heating on upstairs. Downstairs brassic.

Quite surprised as I didn't think the boiler would function under gravity...

Hello Dan

Thank you for your two posts - can you explain why you think the pump is kaput? I am inclined to agree, I think, but I'd really appreciate the explanation so that I can follow the logic of it.

Many thanks
 
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Because it sounds like you're pump is starting to seize after 30 odd years. If the pump can't move freely enough it's going to get very hot. Especially that you said some steam came out.
Its my day to day job getting heating up and running, pump would be in my mind before getting in the house.

If your valves hold on either side of pump its not too difficult, 2 nuts, whip it out and swap the wires over.

Edit: A good rule I always go by, get the heating running, pump running, open the screw cap, if you can stop the pump with big screwdriver you know its weak and needs changing.
 
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I concur. Next week I am chasing a neighbour's pump. Totally dead, but got water and heating on upstairs. Downstairs brassic.

Quite surprised as I didn't think the boiler would function under gravity...

Hello Dan

Thank you for your two posts - can you explain why you think the pump is kaput? I am inclined to agree, I think, but I'd really appreciate the explanation so that I can follow the logic of it.

Many thanks


From reading your description and applying 16 years of repairing, designing and installing heating systems (preferably in that order).
 
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Because it sounds like you're pump is starting to seize after 30 odd years. If the pump can't move freely enough it's going to get very hot. Especially that you said some steam came out.

Thanks JMGas - but I've never once said that steam has come out of anywhere! This is why I am asking for an explanation for the diagnosis. A new pump is 150 notes, and I would be more than a little frustrated to buy one, fit it, and then find that it was actually something else and have to start over from scratch - all the time having a cold house downstairs... I don't think it's unreasonable to ask why a poster thinks that the diagnosis is correct is it?

Are you saying that it simply couldn't be anything else?
Or are you saying that it could be something else, but your "gut and experience" tells you that it's most likely to be the pump in your opinion?

If the pump is kaput and seized, I don't understand why I am still getting blistering hot pipes on all of the outlets of the diverter valve, when the pipe from the pump is relatively cool - how can this be? This doesn't make sense to me...

Again, the pump is kaput, when I opened it up and twisted the spindle with a screwdriver and it turned both ways, this doesn't seem to support the fact that the pump is seized?

This is why I am asking for more information... I trust you understand?

If your valves hold on either side of pump its not too difficult, 2 nuts, whip it out and swap the wires over.

Thanks again, but one would assume I need to drain the system down first? When you say, "if your valves hold on either side of pump" - what exactly does this mean?
 
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Ah misread steam for stream.

Holding means that the valves are actually working and stopping water flow. You don't need to drain the system if your valves work, but them being 30 years old I wouldn't count on them doing their job.
Also, being able to move the spindle with a screwdriver only proves its not 100% stuck, not how efficiently its working
 
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