Catch 22

[Jamthesun]

Hi Guys,

I hope you can help.

I have a large system of 20 rads, 2 of which are large towel rails. One of the towel rails is on a little run-off circuit. The boiler is a glowworm Ultimate and the pump is a Grundfos 15 60. The system was power flushed last year.

The reason for the flush was because the run-off towel rail wasn't getting hot - just warm (it had been fine but was deteriorating). The flush didn't solve the problem.

here are the symptoms we have now:

1/ The run-off towel rail is completely cold the pipe feeding it is tepid.
2/ The extremities of the system don't get hot.
3/ If we turn the boiler up high it cuts out - not immediately but regularly. Often wake up to a cold house. We have to keep it at about 50% to prevent the overheat cut out. When we do turn it up the extremities of the system do get hot.

All the valves and controls seem to be working fine and the water is hot.

Thoughts I've had:

1/ The pump is not pumping effectively hence cold rads at extremities. Maybe this is responsible for the boiler overheat too i.e. water not moving through the boiler quick enough?
2/ The pipework to/from the run-off (which is 15 mm branching off a large pipe before the valves) is blocked hence the overheat problem. The pipe to the rail is warm but it doesn't warm beyond the valve. The pipe away is cold.

Any ideas?

 

[doitmyself]

The system was power flushed last year.

Was the system re-balanced after the power flush was done?

 

[Jamthesun]

It was yes.

The run-off rail is closest to the pump so I shouldn't it get hot anyway?.

 

[on31ll]

is the system still clean if water is drained off ? and inhibitor was used ? and enough of it since yours is a bigger system ?

 

[Jamthesun]

The water that comes out is a light brown colour.

 

[Rickster123]

I would take the towel rail out and flush it through manually. Far more effective in my opinion. how old is the pump?

 

[on31ll]

suggests that the system isnt properly cleaned and if the system did have inhibitor then possibly not enough was added. do you have trvs on the radiators ? if you turn all the radiators off on the system except towel rad does it get warm ? and you have tried bleeding that radiator ?

 

[Jamthesun]

I would take the towel rail out and flush it through manually. Far more effective in my opinion. how old is the pump?

The pump is about 10 years old.

 

[Jamthesun]

suggests that the system isnt properly cleaned and if the system did have inhibitor then possibly not enough was added. do you have trvs on the radiators ? if you turn all the radiators off on the system except towel rad does it get warm ? and you have tried bleeding that radiator ?

I've tried bleeding the radiator water comes out no problem. I'll try shutting off the flow side and bleeding and see what happens.

I assumed the brown was inhibitor. It's clear not sludgy.

There are TRVs on some but not all radiators. The furthest ones that are the coolest don't have TRVs.

 

[on31ll]

if the system is clean etc then it sounds like maybe the pump. but i would try shutting down the radiators with trvs to see if the pump pushes wather to the 'extremties' of the system.