One radiator will not stay hot

[Last Plumber]

I think you need a Heating Engineer to assess the pipe work and rad sizes before you do anything.
I wouldn't personally 'try' changing the pump because it won't be cheap and it may not be necessary.
Different sizes of pipe deliver different flow rates per hour. It is possible that 15mm is undersized and that would give the symptoms you describe.

 

[townfanjon]

Has this just happened ,did you inherit the system , did it work correctly before ?

 

[Jason Hill]

Thanks once again for all your replies. To answer each query, the entire system was a brand new install in 2005 with all brand new pipe work being above ground. The pipe work from the boiler is 22 mm but it all becomes 15 mm as it feeds into the radiators. All exposed pipe work is 15 mm and the living room one is fed by 15 mm pipes from other rads. All the rads are original standard type from the install in 2005. The problem has not always existed. Is it time to call out a heating engineer. Thanks again, Jason

 

[townfanjon]

Thanks once again for all your replies. To answer each query, the entire system was a brand new install in 2005 with all brand new pipe work being above ground. The pipe work from the boiler is 22 mm but it all becomes 15 mm as it feeds into the radiators. All exposed pipe work is 15 mm and the living room one is fed by 15 mm pipes from other rads. All the rads are original standard type from the install in 2005. The problem has not always existed. Is it time to call out a heating engineer. Thanks again, Jason

If it worked ok from day one , it cant be pipe sizing , gut instinct as I have said earlier is probably the pump , we have a way of testing them lol , but I wont tell you how , please report back on any findings.

 

[Jason Hill]

Thanks for all your advice. I will update the thread when I have got an engineer out. Jason

 

[dan_the_plumber]

My living room radiator is cold when all the other radiators are firing. I have checked all the internet YouTube advice feeds. The trv is working correctly, the lockshield valve is also working and I have taken the radiator off and flushed it through and have bled it. I believe it is the furthest from my combi boiler. I have turned all my other radiators off and this makes the living room radiator work, but as soon as I turn one other radiator on the living room one goes back to cold. Any further DIY advice would be much appreciated. Thanks Jason

Have you had your system converted? Probably from a back boiler to a combi? Or from a boiler in one part of the house and your new boiler re-sited?
Sometimes plumbers connect into the 15mm branch, instead of connecting back into the 22mm 'source' pipework.
This can result in balancing issues too bad to 'fine tune' by adjudting radiator valves alone.

 

[Jason Hill]

As previously mentioned the whole system was newly fitted in 2005. There have been no further updates or additions since then apart from the current boiler being fitted in 2008. Thanks for your question. I'm still waiting to get hold of an engineer. Thanks Jason

 

[Dkdc71]

Try and remove the trv head and see does it make a difference they can play up sometimes as someone previously said if it worked from day one it's a process of elimination good luck with it