Only heat 2 radiators upstairs after changing motorised valv

[shinares]

Hi,

I managed to fit the new motorised valve for the central heating. After I fit it in, I tested by turning on the central heating and hot water at the same time (BAD IDEA !!!). The pressure valve (the red thing?) made lots of noise and the water and the radiator didnt become hot. So I bled the water heater and now the water heater is working perfectly.

Assuming I can just solve the problem using the same method, I bled one radiator upstairs (the furthest radiator from the boiler). The radiator didnt give any hissing sound and instead it was just splashing with cold water. So after googling around, i found out that it may require further bleeding process which then i did it by plugging off the pin on the radiator. After a few litters of water, the water came out warm. So then I plugged the pin on on the radiator and try to turn on the hot water from the controller. And the radiator is still stone cold. Funnily enough the other 2 radiators upstairs just need an air bleeding for a few second and it works perfectly. Meanwhile the radiators downstairs are all cold. I used the same method of bleeding a few litters of water and all of them are still cold. All cold radiators splashing cold water when i try to bleed them.

I googled more about this and ive tried and failed the following methods:
- turning off all radiators and let the problematic one on
- try to 'balance the system' by opening both valves on each radiator
- turn on water heater and then turn it off then turn on the central heating
- make sure the water supply in the small tank in the loft is full

I suppose this should be an easy fix but its been 3 days ive been trying to fix this problem and failed any suggestions please ? Thank you

 

[45yearsagasman]

Post a pic of your cylinder etc, especially the red thing. You may have a sealed system.

 

[shinares]

Hi 45yearsagasman,

This is actually the continuation of this problem: //www.diynot.com/forums/plumbi...-turn-off-the-central-heating.364284/#2761878

The picture of the red thing (pressure valve)?

I tried to bleed the cold radiator upstairs yesterday again but its still cold. The pipe lead to the radiator was getting warmer (but the radiator still cold) while I bled litters of water but after I stopped bleeding the radiator, the pipe becomes cold very soon (and of course the radiator remains cold)

Any help please ? I thought this problem suppose to be quite a simple

 

[JohnD]

when did you balance the radiators?

the purpose of bleeding is to get air out, there's no point in bleeding out water.

 

[shinares]

Hi JohnD,

I tried to balance the system after I bled the cold radiators (I bled starting from the furthest one upstairs).

Now I closed both valves on each radiator except the cold radiator upstairs.

 

[JohnD]

is the pump running, and are the pipes on each side of it hot? how far are the pipes hot?

is the pump hotter than the pipes?

 

[shinares]

Hi JohnD,

Thanks for the reply.

1. is the pump running? I suppose so because it makes a bit vibration and also since two radiators upstairs are hot and the hot water also works fine i assume the pump is working ?
2. are the pipes on each side of it hot? yes the pipes are hot
3. how far are the pipes hot? when I turn the hot water or the central heating on the pipes are hot all the way including the pipes after the motorised valves
4. is the pump hotter than the pipes? Yes its hotter

 

[JohnD]

4. is the pump hotter than the pipes? Yes its hotter

this is a bad sign. It happens when the pump is jammed. Take out the silver screw in the middle (with all power off) and see if you can turn the spindle with a screwdriver. Water will not squirt out, though there may be a slight drip.l

you say only two of the upstairs radiators are hot.

If the downstairs radiators are all cold, it suggests the pump is not working. Water will circulate (slowly) between the boiler and an upstairs radiator even with no pump.

 

[shinares]

Hi JohnD,

Thank you for the suggestions. I did what you asked and I found the spindle spins well when the pump was off. I also tried to check the spindle when the pump was on and the spindle still spins well. Any other method to check the pump ?

Yes the radiators downstairs still cold and so as one of the radiators upstairs. Ive googled many similar problems and I can conclude that only the pump or the unbalance system.

Because the pump is quite expensive (around £100), Im thinking to try to balance the system (again) perhaps previously I did it wrongly. Just to confirm the balancing process :
1. Turn on the central heating (without hot water)
2. open fully the thermostat on each radiator
3. turn the lockshield valve off and then open it only 1/4 of the turn on the radiators upstairs
4. open the lockshield valve fully on the radiators downstairs

Am I doing this correctly ? Thank you

 

[JohnD]

old pumps are sometimes worn and clogged, you can take it off and inspect using the pump isolating valves on each side, but I don't think that is the probable cause of your troubles.

Feel along the flow pipe from the pump to see where the heat is going. It might be that you have a bypass allowing the flow to miss out the radiators, or it might be that the HW valve is allowing it to go to the cylinder (this will result in unusually hot taps)

 

[shinares]

Hi JohnD,

I didnt expect a reply at 12am so I really appreciate your reply. I followed the pipes and found both sides of the pressure valve and motorised valve for the central heating are all hot. From the motorised valve, the pipes go up and i can see those branches out. I checked all the branches and they are all hot.

For now I cannot check the connection between the HW as you mentioned since I heated up the water just now so it will be hard to tell the difference.

Anyway, i have set to balance the heating system following the step-by-step. I will post if there is anything changes. If not probably the pump is not functioning properly. I noticed the body of the pump is very hot that I cant even touch it so there is a good case that the pump is the culprit.

 

[shinares]

Hi JohnD,

After spending 4 hours trying to balance the system using the step-by-step, the previously cold radiator upstairs now hot however the one of the previously hot radiator upstairs becomes cold.

So can I safely say the pump is broken ?

 

[D_Hailsham]

Just to confirm the balancing process :
1. Turn on the central heating (without hot water)
2. open fully the thermostat on each radiator Remove the head is better
3. turn the lockshield valve off and then open it only 1/4 of the turn on the radiators upstairs 1/2 turn is a better starting point
4. open the lockshield valve fully on the radiators downstairs Do exactly the same as upstairs - 1/2 turn.

This will give you a starting point.

You now have to 'fine tune' the system so the temperature drop across each rad is approximately the same (11C). The 'scientific' way of doing this is to use thermometers, but you can get acceptable results using your hand. It's the cooler (return pipe) which is the important one; they all need to feel about the same temperature.

Check each one and then choose one which is midway between hottest and coldest as the 'standard'. The LS valve on any rad with a colder returns needs to be opened a 1/12 of a turn; rads with hotter returns should be closed a 1/12 turn. Leave the rads to settle down for 15mins; then check again and adjust any still too hot/cold. Repeat if necessary.

 

[bazdaman]

You will probs need some inhibitor in now aswell if u have drained anything and bleeding water out of rads dilutes the mix

 

[shinares]

Hi d_hailsham and bazdaman,

Thanks for the suggestions. Will try it sometime next week and will report back here.