Is it the pump?

[bodgeitandsee]

hI

Already posted for help after having a boiler airlock which is now OK.
I have a 30 year old system (fully pumped - vented CH) with a 17 year old boiler and suffer cold bottom rads (2 x 2200mm double each with saucer sized warm areas in top corners and that's it, all others as bad).

Currently running a litre of Fernox Heavy Duty Restorer to try and sort it.
All TRV's (ancient MMA ((??)) looks like a joined up logo on valve body not TRV cap, can post a pic if needed) all set to max.

Could it be that the pump is losing it's efficiency - Grundfos 15-50, it is in the loft above the lounge and sometimes sounds as though it steps up a gear, this happens even during a boiler continuously on period so it's not switching.

I have just opened the lockshield on the bathroom rad by three quarters of a turn and the bottom of the rad is now hot which makes me think it's a criculation problem.

Also the furthest rad from pump has it's LSV fully open and barely loses it's chill. Can't turn down any earlier ones because they're not warm enough themselves.

The pump sounds were happening prior to drain and refill so it's nothing that I've caused. Would also say the system water looked fairly clear when drained, certainly not sludgy.

Any ideas how to get the caps off these decrepid old TRV's?

Thanks for any help.

 

[shaka]

Do your self a favour 30 years old invest in new system go onto www.mrcentralheating buy new system get someone to fit it system inc pipes valves under £800

 

[ChrisR]

Sure, or move house.

Yes I'd change the pump. Sounds like that go with slow-runners.
If not much help then remove a rad and see if it' has a lot of black thick liquid in it - flush it with a garden hose. You can do a partial flush by connecting hoses to rad tails (garden hose sending mains in one connector and out of the other) and opening one rad at a time until the water flows clear. Best with some air in the rad as you flush each one. You should cap the pipes at the f & E tank but may not need to - at least make sure the overflow is going to work!
That isn't a powerflush but it can transform a ground floor's heating.

 

[bodgeitandsee]

Now it's obvious that I'm no heating engineer or I wouldn't be asking advice on here.

If I change my pump could I buy a higher capacity one or am I up against the boiler keeping up then? Ideal W RS 450 Output 40,000 to 50,000 btu Input 52,900 to 65,400 btu.

The boiler will be changed next spring so would it be an idea to have the next step up boiler and pump so there is larger volume of hot water being shifted.

Will also change all the rads. For a start I don't need 2200mm double in a 5m x 5m (8' ceiling) bedroom do I? There are others in the house that are equal overkill. I'm in a brick cavity wall 3 bed bungalow without cavity wall insulation and don't want it and have poorish loft lagging of varying 70 to 100mm but will top that up when I get a chance in the next few weeks.

 

[slippyr4]

If I change my pump could I buy a higher capacity one or am I up against the boiler keeping up then? Ideal W RS 450 Output 40,000 to 50,000 btu Input 52,900 to 65,400 btu.

If your pump is too small/slow, then you can't push enough heat from the boiler to where it's needed.

If your pump is too big/fast, then it'll be noisy.

There's no real point oversizing the pump. You might as well get a like-for-like replacement.

If you do choose to try the recommended garden-hose-flush, you can get push fit to hose pipe connector adaptors from plumbers merchants. These are dead useful for the job in hand.

But it does sound like you've got a knackered pump which is trying to push treacle round your system

 

[JohnD]

Will also change all the rads. For a start I don't need 2200mm double in a 5m x 5m (8' ceiling) bedroom do I? There are others in the house that are equal overkill.

no need to put in smaller rads, you just need TRVs that work so the room doesn't get overheated.

 

[bodgeitandsee]

The 2200 doubles don't get fully heated anyway, just the top corners. I really feel this is a flow problem though rather than a rad 90% full of sludge.
I'll change all these old unknown TRV's for Drayton TRV 4's and see how they work. Could it be the TRV's are knackered and preventing the flow? Can't see how to get the tops off them though.