boiler going out after radiators changed

[shd1970]

right then, update.....

boiler was on for approx 20 mins and 3 out of 4 radiators upstairs got very hot in deed, 1 still luke warm though. Bled it - no air worth speaking of.

downstairs, 1 of me new rads got warm, the other 2 new ones didnt and the final radiator was still cold.

so, does this still imply an airlock and if so, should i just keep firing up the system, bleeding the rads and the pump until the central heating stays on ?

 

[JohnD]

your radiators probably need balancing.

For a start, turn the hot ones off and see if the cold ones heat up. If so, adjust the hot ones so that they are only on by a fraction of a turn.

There are fuller instructions somewhere but I can't find them.

Keep bleeding to get the air out.

If you got black water, or black sludge out, consider spending £100 on a Magnclean. I guarantee you will be amazed and delighted to see how much black sediment it can trap.

 

[Goldspoon]

Can you turn pump to a higher speed? Try it.

 

[shd1970]

thanks again John - i'll try the balancing

can you tell me please, is it normal then that the boiler keeps going out ?
is this a safety mechanism to stop heat build up ?

even though the boiler goes out there is still a fair amout of noise from around the pump and associated pipes.

further info for you that i have 4 rad down stairs of which i have replaced 3.

the 4th one is still cold and as it has been a while since the system, i was wondering if it could be blocked ?
the bathroom rad that feeds the 4th rad was luke warm but now gets hotter so i'm wondering if it will filter down and give the cold rad a "nudge".

not entirely sure why only 2 of my 3 new rads are getting warm tho.....they all have Drayton TRV4 valves fitted and are all turned to MAX and the lockshield outlets are fully open

 

[JohnD]

the boiler will turn off when it reaches the temperature set on its thermostat.

if there is an easy path for the circulating water to take (through the hot rads) it will tend to go that way and not through an alternative ( more difficult) path. So the point of turning the hot rads off or down is to make that path more difficult, so that the flow has no alternative but to go through the cold rads.
http://www.diydata.com/projects/centralheating/balancing/radiator_balancing.php

It is still possible that you have air in the pipes. Or you might have a blockage from old sediment, especially if it is an old open system and you did not bale out the mud from the F&E tank and sponge it clean before draining and refilling.

If you have added new pipes onto old ones the design may be wrong, especially if the pipes are small bore.

If it was me I would turn the pump speed up and the boiler stat right down so that water squirts round without the boiler getting hot. I have sometimes find that bubbles come out if you keep turning the pump off and on by moving the wall stat up and down

If you ever find the pump is hotter than the pipes, water is not flowing through it.

I am still not clear what happens when you bleed the highest radiator.

I am not a pro.

 

[shd1970]

Hi all

i can confirm all radiators are now "hot hot hot" except the one downstairs rad that wasnt drained and hasnt been replaced.

as its a drop feed, i suspect its gunked up.

i've bled it loads and got a stack of cold / amber coloured water out.
the feed supply is now warmish so i guess its just gonna take a few goes to get what ever is in there moving.

once it gets hot, plan to run the system for an hour or so before draining and then add Fernox F3 cleaner to run through the system for a few days.

Boiler seems all ok now

thanks once again for all help earlier today

 

[JohnD]

turn off the hot ones.

chemical cleaner will not work if there is a blockage as it will not flow into the problem area.

 

[shd1970]

further bleeding of the rad and following of your advice John of closing the other rads has now got the offending rad hot !

will fire up again tomorrow, get the whole system hot and then drain and add cleaner for a few days.

thanks for your input....appreciated !