Upstairs Radiators Hot and Downstairs cold

M271

I have noticed for the last few months that the radiators have been slower to heat up especially when the hot water is also heating, but from this morning the downstairs radiators are cool (some are barely 'off cold' at the top corner) but the upstairs ones are hot. My system is an open vented system.
I turned off the radiator themo valves off upstairs and the downstairs ones then did heat up but not to a very hot state.
After reading items online I have vented the Grundfos Pump (did hiss a bit but momentarily as I unscrewed it) and checked that the expansion water tank in the loft had water in it and it did.
My uninformed conclusion is that either the pump is losing its power (11 years old) (it is making a quiet grating or aeration sound with no vibration), or that there is an airlock somewhere in the heating pipework.
Another point is that even when I have only the downstairs rads on (and are warm not hot at best) that the return pipe to the boiler is very hot so the boiler modulates and doesn't work hard enough to properly heat the radiators.
Any ideas what it might be or what I can try next?

Mr.Generous

Balancing the system.

First vent all the rads while its off.
Second check your pump is on the highest setting, switch often on the pump its self.
Third turn all rads downstairs on full, both sides - thermos valves and lockshields.
Next turn rads upstairs right down. Fire up system.
Check rads, downstairs should get hot. Turn up upstairs bit at a time until also hot.
If its not been done for a while consider a flush out and re - fill of the system, do it a few times and then put inhibitor in for final fill.

happybiker

Pumps gone. very common symptoms. The return pipe is getting very hot due to receiving residual heat from the boiler. that shows a lack of circulation. upstairs rads getting warm through convection. downstairs have no flow.


Yup, you need a new pump. if the system has worked ok and has not been disturbed, ie. rads removed for decorating then balancing will not need to be carried out.

M271

happybiker wrote: »

Pumps gone. very common symptoms. The return pipe is getting very hot due to receiving residual heat from the boiler. that shows a lack of circulation. upstairs rads getting warm through convection. downstairs have no flow.


Yup, you need a new pump. if the system has worked ok and has not been disturbed, ie. rads removed for decorating then balancing will not need to be carried out.

Thanks, no nothing has been disturbed and rads have been in balance (within reason) for many years. As the pump is 11 years old I might as well change it anyway, although I have read the Grundfos pumps often last for many more years then that, however mine is on the highest speed and serves 15 rads in a large 4 bed house so may have worked harder!

M271

Update to my original post,
Yesterday turned upstairs rad off while living downstairs for the day, downstairs rad were warm, hot water I switched off. During evening realised that downstairs rads had gone from warm to hot, hour before bedtime opened upstairs rads and expected downstairs rads to go off but they did not, all rads up and down were hot, hot water still switched off.
This morning all rads came on (happy days!!) HOWEVER when hot water came on downstairs rads went cold and upstairs rads went warm from hot. Its as if the system cannot cope with all demands.
So I'm thinking is it really the pump (rads were OK last night), an airlock, diverter valve or what.
Any further thoughts from anyone?

M271

LATEST UPDATE:
Soon after my last post the heating packed up completely. Called in emergency house breakdown company and told them about probable pump failure, they replaced it with new Grandfos pump and been working OK since (well the pump has!). The 15 rads now all over the house get hotter and quicker than ever before (been in house for nearly 19 years), even with the pump set on the lowest speed setting. Pump was originally set at the highest setting but the low frequency resonance in the pipes drove me nuts, even at the lowest setting the resonance droning in the pipes and transmitting to the house is annoying but I'm in the process of trying to stop the pipes setting off the resonance by removing contact to the walls, floors etc. I don't know if this problem is common with modern more powerful pumps, just seems to be a different frequency that sets my pipes/house off!

I now have another puzzling other issue where the heating stops cycling and cuts out after working for several hours but I will post that on a separate thread.