working boiler, luke warm rads and hot water ok

[Nick B]

i have a worcester gas boiler that has recently been serviced and a replacement pump to a 10 year old system. Thermostat and 3 way switch seems to work fine. Heating up to the hot water ok to the tank, but cannot get more than 4 out of the 9 radiators anything more than moderatly warm no matter how we balance them. Each individual radiator can be made hot by adjusting the balance and all radiators have been bled. The return pipe at the boiler never gets very hot. is there a likely cause?

 

[craftor]

I'm just a diyer, but could be the pump might have been fitted with the flow going the wrong way
If your system was working ok before the pump change I would check this out first

 

[Nick B]

it wasnt working properly before i fitted a new pump .

 

[simond]

Take the actuator off the 3 port valve and select heating manually, using the brass valve spindle. Has been known that the valve is only just opening a tadge to CH, rather than fully, causing low water flow.

 

[Nick B]

there seems very little movement in the spindle, can you tell me how many degrees they roughly rotate?

 

[craftor]

Butting in on Simons reply, should be about 30 degrees and should turn freely. Try turning on the CH and see if the actuator works
If you don't get any heat to all the rads after turning the valve manually the problem I think is elsewhere

 

[Doggit]

Why was the pump changed, and did you see the colour of the water in the system when it was done. The pump speed may not be high enough, or there could be a blockage in the system - or the 3 port valves not opening sufficiently - but that could cause the boiler to keep cycling . Do the rads get hot at the top, and are cold on the bottom. If the flow and return pipes are hot, that suggest the boiler and the pump are working, but the heats not getting in to the radiators. Try turning only the closest rad to the boiler on, and all the others off, and then let us know the results.

 

[Nick B]

ive changed the 3 way and actuator but there is no change.
i have tried shutting all the rads off opening one nearest boiler first and then all subsequent ones individually. they all get hot evenutally from the top of radiator down and after several minutes the return pipe at the boiler gets warm but not hot enough you cant hold. Drained down water seems largely sludge free if a little grey here and there.

 

[Doggit]

From you're description of how the rads are heating up from the top down, it suggests there's sludge in the rads - and very likely in the pipes as well. You'll need to get some cleaner in the system for a couple of weeks, and then take each rad off in turn, and flush them out; then flush the pipework out for good measure.

 

[Nick B]

ok i will do that! many thanks for your advise

 

[Nick B]

just an update - took every rad off wall into he garden, flush out loads of sludge. Put them back put in the solution for a couple of weeks and bingo we are back on full working order - many thanks

 

[Doggit]

Thanks for that Nick, nice to get some feedback occasionally.