upstairs radiators hot, down stairs cold

[sammyc]

hi people
i have a saunier duval f23e combi boiler(11years old), a few days ago i tried to turn on the central heating but the boiler kept on igniting on/off. the hot water works fine.my service people came out and checked it and said it had a build up of magnitite in the water for the heating and to get it power flushed which i did the next day. home serve came out again and still no luck, so the engineer changed the pump and heat exchanger, now the upstairs 3 radiators work but the remaining 4 downstairs are cold where the boiler is. he said there is nothing else he could think of as the boiler was doing its job and hot water was heating upstairs radiators but the return pipe in the boiler was cold indicating mabey there is still a blockage in the radiators/pipes and mabey get the power flush people out again and also to change the radiator valves as they are old and may be blocked.
any thoughts are welcome by a newbie,
thanks

 

[sammyc]

anyone with any suggestions??

 

[Gary Kinvig]

Hi im not a qualified plumber yet but have come across a similar problem, have to rads been balanced?

 

[SimonJohns]

You have an air lock

Turn all rads off that work. Be that the trv or lockshield

Wait for a rad to start to work. Then turn them off as they start to work

Once all have started to work( by this point all rads but one will be off)

Turn all back on, remembering how much you turned the lockshield off. E.g 7turns

Give that a try

 

[dontknowitall]

It's a classic symptom of the pump not working. You say you've had a new pump put in but is it working/has it been installed correctly? Could well be an airlock (as suggested by SimonJohns). If you close the rads as suggested and they still don't warm up then it's back to the pump.

 

[sammyc]

hi, i have no idea how to balance rads, so they have not been done

 

[sammyc]

im getting a plumber in soon, who said he will take off all rads and power hose them and replace valves with therms, and finally power flush again. i will suggest to him to balance rads?. i dont think its the pump as valliant group engineer has replaced pump and heat exchanger with original parts, i watched him do this. ps the rads and valves are about 28 years old.

 

[sammyc]

can anyone also explain why when turning on the heating on the boiler do the flames ignite for about 15 seconds and then goes out for about 2 minutes before igniting again for 15 seconds, it does this constantly.

 

[shorticus]

can anyone also explain why when turning on the heating on the boiler do the flames ignite for about 15 seconds and then goes out for about 2 minutes before igniting again for 15 seconds, it does this constantly.

The boiler is protecting itself, there is very possibly a flow issue (see previous answers for most probable causes), basiclly there'll be a thermister (temperature sensor) on the flow from the heat exchanger which is read by the pcb, if the pcb thinks that the flow is too hot then it'll turn off the gas supply to protect the heat exchanger from over heating...if you've had a powerflush and new pump fitted then maybe the thermister has lost calibration but I doubt it, this is a very quick test for an experienced technician with a multi-meter just to eliminate it, I'd be inclined to agree with @don'tknowitall and my attention would be with the pump and/or airlocks

 

[sammyc]

please clarify, an engineer is coming on monday to take off all rads to clean, at the moment they have lockshiekd valves on both ends, these have not been touched for about 20 odd years, after cleaning the engineer wants to put trv on flow end on all rads. Ive never needed to use these as ive never had problems with rads before, now is it necessary to use these (i dont have a thermostat as temperature is controlled from boiler) or can i just replace old lockshields on both ends with new lockshields. Also as my pipes are about 28 years old i think its the single pipe system and i dont really want to chance pipes because of access to floorboards and expense.
your thoughts are appreciated.

 

[dontknowitall]

You need to fit TRVs, room thermostat (and hot water cylinder thermostat if you have a hot water cylinder) to comply with building regulations and this process will lower your carbon footprint on the planet (which is the reason for the building regulations).

 

[sammyc]

just an update, the engineer came and changed all the radiator valves, took off the rads and powerflushed them individually in the garden, amazing how much sludge had built up and sludge in the old lockshields we also banged on the rads whilst flushing to loosen hard sludge, With all rads off and new lockshields attatched to rad pipes we power flushed again and during this checked each flow and return pipe to make sure water was getting through, on reattatching rads we filled the system and released any air and then turned on each rad one by one all upstairs are hot the first in the chain downstairs is also hot but the last three downstairs are luke warm. I have been told the rads may need replacing because they are about 20 years old and there is a certain amount of sludge that will allways remain in rads. what do you think?
I have also noticed that when you run the hot domestic water the rads also seem to be getting hot, is this a possible reversing valve problem? Ive got the homeserve engineer coming on friday for this fault.

 

[arran197]

Sounds like a flow issue to me. If the rads are getting hot when the hot water is on, then the diverter valve is no good, which is probably the reason why the rads aren't heating up. It's probably stuck in the dhw mode with enough of a gap to allow the few rads to heat up. I had a similar issue the other day, but it wasn't the diverter, it was a gate valve on the heating flow pipe, (which is very strange)!

 

[PowerFlushAssoc]

Pump - eliminated
Radiator valves - likely

If not valves:
power flushing can only remove sludge if it is loose and small enough to pass through the narrow parts in the system, like radiator valves.
If you have large pieces of sludge stuck in the pipes, the only way is to remove the radiator valve/s. Connect a hose straight on the pipe (valve is too narrow) and pressurize the rest of the system pushing the large pieces out.
If one power flush fails, the second one is likely to fail as well; unless the guy doing the second flush, spots an obvious mistake the first guy made, which is not likely.
Sometimes power flushing is recommended when old fashion plumbing is needed.

 

[folwlerg68]

on your last post i see you say you,ve got a single pipe system,then i would definetly say you,ve got a blockage or air lock. as stated earlier if you try turning all valves of on rads that are working and bleed the other rads as well as pump you may clear blockage and also with a single pipe system it is important to balance system i.e. 1st rad on system will not need to be open very far as this will be hottest and furthest rad away from boiler will need to be open most. you do not have to have trv.s you can just put lockshields on if you prefer. cheers grant