Three upstairs radiators not heating

[neophyte]

Hi,

Have moved into a new house before Xmas and heating switched off for two weeks prior. Since moving in three radiators upstairs (perveived to be last on circuit) will not heat. Have flushed all rads, drained and refilled system. Still no heat. Have bled all rads too. Finally yesterday I switched off all rads in house leaving only the three cold ones on. They heated but I notices the expansion tank in attic filled to overflow pipe, both in and out rad pipes were hot and I had the feeling the heat was coming in from the return pipes. Also when all other rads were off and I bled the three air was being sucked in, not blown out????

I have learnt all I know from searching the forum in the last two weeks so am a complete novice. Have also had a plumer call who was confused by the situation and left without charging!!!!

Previous house owners assure us all was working fine when they left the house since their young kids were sleeping in these rooms.

Any help greatfully appreciated

 

[oilman]

This is suspiciosly like a blockage in a pipe, but you have drained and refilled, and if the plumber left without charging, we will struggle to come up with the answer.

 

[BDL]

What system do you have?
Is your pump running correctly?
Have you bled your rads?
Try turning off all rads that are working and leave the affected rads on, do they heat up?
What type of motorised valve do u have? 2 2 ports or a 3 port?

Might be worth calling in a Corgi heating engineer as opposed to a plumber?

 

[neophyte]

Thanks Oilman and BDL for replying.

BDL, in answer to your questions,

I have a Potterton Kingfisher boiler on an open vented system

As far as I am aware the pump is working fine

All radiators have been bled but when the heating is on the three cold rads suck air in so consequently I find that I can only get this air out by bleeding the functioning rad on the landing. Once heating is off these three radiators can be bled ok.

I have turned off all rads save the last three. They did heat up but the expansion tank filled to the overflow tank with hot water. Also I did this again yesterday evening since posting this message and whilst at the expansion tank I heard a noise from the vent pipe and then water was forced by what sounded like air shot at high speed from the pipe into the tank and caused a tidal wave to splash up and hit the roof beams. This scared me so I then returned everything back to how it was and left it for the evening.

I have no idea what type of motorised valve I have or how to identify it, sorry.

In my naivety the plumber I referred to was a Corgi registered heating engineer.

If you have any other advice I would extremely grateful.

 

[marios_kin]

If I remember right the system was off or drained for a couple of weeks. I have come across a similar prob but not as drastic. Firstly turn the boiler thermostat down when you isolate the working rads this should prevent scalding and over heating.
Look at the pipes coming from the expansion tank, if I am on the right track it will drop vertically and the have an elbow and go horizontal. (it will also be 15mm or smaller bore)
attatch a hose to one of the down stairs rads drain cocks, isolate the water supply to the loft tank, then open the drain valve. When you return to the loft tank I will be surprised if the water level is dropping.
If this is the case then the blockage in your system will be at the aforementioned elbow. Very carefully tap it (don't break it) once water starts flowing from the loft tank, turn off the drain. add some descaler and top up the tank. Leave it in the system at least a couple of days but no more than 6.
Check for leaks. Then drain and refill 5 or 6 times to flush it all out. On the last fill add some inhibitor.

PS never bleed with the pump switched on.