Is my heating circulation pump knackered?

[Robert Irons]

Hello all, been a while since I used the forums!

My house has a n F&E tank central heating system with a grundfos aplpha 2 pump and fairly new worcester greenstar ri boiler. For as long as we've lived here Ive always had to run the pump on speed III in order to get heat to distribute to the radiators in the house, and even then was fairly puny down stairs. A few weeks ago I drained the system down - cant even remember why now....After filling up again I initially couldnt get the heating or hot water to fire. Cycling the pump low to high speed and manually releasing air locks around the 3 port valve seemed to help and eventually got the hot water going and the heating vaguely warm. However when heating is on the boiler cuts out repeatedly. The flow pipe from the boiler is always v hot and the return pipe is cool.

As the days went by the heating became gradually worse with downstairs rads getting cooler and cooler and the upstairs not as hot as they used to be.

I had a plumber round as I need some pipe work changing anyway that I couldnt be bothered to do myself - and he reckons I have two problems:

1) At some point in the past our separate feed and vent pipe has been converted to combined feed and vent - resulting in more air locks - so he recommended the original design was re-instated
2) Pump might need replacing

Not wanting to wait till after xmas to have a bit of warmth and being a little doubtful over the benefits of reinstating the separate feed and vent pipes - I decided to reinstate the separate feed and vent pipes myself. I then backfilled the system via the draincock , drained again and then backfilled again and added central heating cleaner. The system was always slow to drain and since backfilling and flushing it now drains alot quicker, suggesting there was a lot of sludge, some of which has now shifted.

However after all this the system performance is if anything worse. I can get the upstairs rads to get moderately hot but none of the downstairs rads are coming on really. Ive recently realised that three of the large downstairs rads are on a drop and these are not coming on atall unless every other rad is turned off.

The pump sounds like its working quite hard on speed III, although is a little noisy. When I cycle through the speed settings it is definitely working but I am convinced now the pump just doesnt have the oomph to push water round the central heating circuit.

Before I take the plunge and get a new pump I thought Id see if anyone thought Id missed anything!? Thanks in advance.....

 

[BlueLoo]

Did you take the rads off and flush them?

Is your FEV piping before or after the neutral point?

There is much debate about combined FEVs. I have the same but cannot seem to get decent info as to the pros & cons. They are beneficial in some circumstances apparently.

Bit odd that the plumber looked to change the system configuration to fix a fault when it was working fine previously.

Flush the rads out with a hose.
Look to see what system you have before you recommision it. The Alpha pump is variable speed so your system might not be set up for it in which case you can just use auto adapt or fixed speed.

Modern pumps are strong. Running yours at full pelt is indicative of something not being right.

Don't think you need a new pump. You'd only replace it if it was noisy (bearings) or damaged (impeller). You can clean them manually easy enough.

(Read my sig)

Best of luck.

 

[Robert Irons]

Love this forum - always get good advice with sensible questions!

Did you take the rads off and flush them?
.

I took off the two main problem rads in the lounge and flushed them as they were having TRVs put on anyway. The whole system has had sentinel X800 in for a couple of weeks now
Admittedly when I had to replace a section of 22mm pipe upstairs recently there were chunks of magnetite around 10mm in diameter in it...

Is your FEV piping before or after the neutral point?.

Not sure what you mean - I though the neutral point is determined by where the FEV cold feeds into the heating circuit? The pump is after this point, if thats what you mean.

There is much debate about combined FEVs. I have the same but cannot seem to get decent info as to the pros & cons. They are beneficial in some circumstances apparently.

Bit odd that the plumber looked to change the system configuration to fix a fault when it was working fine previously.

I think his thoughts were that the main issue was that there were some major air locks in the system and that the combined FEV was the cause of this. I thought by back filling I would avoid major airlocks. Also he pointed out that originally the system (installed early 90s) clearly had separated feed and vent pipes as you can see where it was capped. He reckons (being ex british gas) that they had a policy of switching systems over to combined when they werent really designed for it. From what Ive read this was a kind of bodge...To be fair the system has never been working fine I dont think since we moved in. As I said I had to run it on III all the time and there was still one major rad that wouldnt get hot no matter what I did - thankfully its in the conservatory and is a waste of time anyway.

Flush the rads out with a hose.
Look to see what system you have before you recommision it. The Alpha pump is variable speed so your system might not be set up for it in which case you can just use auto adapt or fixed speed.

What do you mean by "what system you have"? Ive been running the pump on fixed speed since we weve lived here.

Modern pumps are strong. Running yours at full pelt is indicative of something not being right.

Don't think you need a new pump. You'd only replace it if it was noisy (bearings) or damaged (impeller). You can clean them manually easy enough.

My thoughts at the moment is to take off the pump with a replacement standing by. If its looks buggered then Id just slot the new one in - any tips on how to visually inspect for likelihood of it actually being ok?

Thanks again

(Read my sig)

Best of luck.[/QUOTE]

 

[BlueLoo]

Love this forum - always get good advice with sensible questions!




I took off the two main problem rads in the lounge and flushed them as they were having TRVs put on anyway. The whole system has had sentinel X800 in for a couple of weeks now
Admittedly when I had to replace a section of 22mm pipe upstairs recently there were chunks of magnetite around 10mm in diameter in it...



Not sure what you mean - I though the neutral point is determined by where the FEV cold feeds into the heating circuit? The pump is after this point, if thats what you mean.



I think his thoughts were that the main issue was that there were some major air locks in the system and that the combined FEV was the cause of this. I thought by back filling I would avoid major airlocks. Also he pointed out that originally the system (installed early 90s) clearly had separated feed and vent pipes as you can see where it was capped. He reckons (being ex british gas) that they had a policy of switching systems over to combined when they werent really designed for it. From what Ive read this was a kind of bodge...To be fair the system has never been working fine I dont think since we moved in. As I said I had to run it on III all the time and there was still one major rad that wouldnt get hot no matter what I did - thankfully its in the conservatory and is a waste of time anyway.



What do you mean by "what system you have"? Ive been running the pump on fixed speed since we weve lived here.



My thoughts at the moment is to take off the pump with a replacement standing by. If its looks buggered then Id just slot the new one in - any tips on how to visually inspect for likelihood of it actually being ok?

Thanks again

(Read my sig)

Best of luck.

[/QUOTE]

I'm not a plumber so just voicing my thoughts.

By system, I'm thinking that having a pump at full pelt means that either the pump or the system is misconfigured.
I've a biggish house and my 12 rads are more than happy on speed 1 (fixed).

 

[Harry Bloomfield]

It sounds as if the entire system needs a very good flush through, to clear out all of the radiators and pipes.

 

[BlueLoo]

It sounds as if the entire system needs a very good flush through, to clear out all of the radiators and pipes.

I couldn't believe the furring up my copper piping had when i had it stripped down this year. Amazing.

I imagine my arteries look similar lol.

 

[terryplumb]

If you removed 10 mm chunks of magnetite from a section of pipe ,it's indicative of the reason you are not getting proper circulation. Your system is probably clogged up.

 

[Robert Irons]

Thanks all for the advice. Ive thought for a while I probably need to pay fora power flush. Thats the specific question I asked the plumber who came round and he sold it as 'dont pay for a powerflush when it may not be the root cause of the problem. Oh look your systems been converted to combined FEV lets change that and replace the pump before we consider a power flush'.....anyway I wasnt totally convinced by his 'diagnosis' hence why ive quickly done the equivalent with the vent pipe myslelf and shown its made no difference. Also as far as I can tell pump is working as its getting up to 42w and then settling on 34w on speed 3 but despite that there still seems too much resistance.

I think this afternoon Im going to quickly attach a hose to one of the rads v near the pump (new pipework) and see how quick the flow is with the system on. That way at least I can be sure its not the pump......

If that shows pump is shifting water at required speed/ volume that reckon a power flush is essential or just wack some more cleaner in (Ive underdosed the system a little this time) and then leave for a few weeks periodically forcing water around the various sections by turning rads off?

What I dont really understand still is why it suddenly became so bad after I drained it - but perhaps that just shifted a particularly unpleasant gob of muck somewhere it could cause all this mischief.

 

[terryplumb]

What diameter Pipework feeds your rads ,is it microbore 10mm or less ,and fed Via manifolds ?

 

[BlueLoo]

Shut the pump valves and turn the boiler off if you are using mains water. You could blow the seals in the pump!

 

[Robert Irons]

15mm pipe work to the rads.

I did not shut the pump valves when filling via mains, but did turn boiler off. I didnt run the mains tap at full blast, just a fairly gentle flow.
How could i tell if the seals have blown? if ive damaged pump during the back filling could that be now causing the poor flow or would just have packed in completely?

 

[BlueLoo]

15mm pipe work to the rads.

I did not shut the pump valves when filling via mains, but did turn boiler off. I didnt run the mains tap at full blast, just a fairly gentle flow.
How could i tell if the seals have blown? if ive damaged pump during the back filling could that be now causing the poor flow or would just have packed in completely?

Ah, you are probs fine if its gentle enough.

The OEM warns you against this practice (at least it does for my pump).

If the seals were blown, you would have wet floorboards

 

[Harry Bloomfield]

How could i tell if the seals have blown? if ive damaged pump during the back filling could that be now causing the poor flow or would just have packed in completely?

Unlikely you have damaged the pump. Fill, drain, fill, drain, fill - try turning different radiators to off, try to maximise the flushing flow through other radiators. If radiators are cold at the bottom, take them outside to flush them.

 

[BlueLoo]

Unlikely you have damaged the pump. Fill, drain, fill, drain, fill - try turning different radiators to off, try to maximise the flushing flow through other radiators. If radiators are cold at the bottom, take them outside to flush them.

I'd just blast the rads outside anyway.
I was gobsmacked with the gunge that came out of mine when i did it last.

 

[Robert Irons]

So just done an experiment - please tell me if you think Im being stupid.

So on one of the flow rad tails I got a flow rate of 16 litres per minute with the pump on full whack
With the pump off I got a flow rate of 10 litres per minute

From this I concluded that the head of water above the tail produced 10 litres/ min of flow, and the pump contributed 6 litres per minite

6 litres per minute equates to 360L per hour.

This is WAY under the specified max flow rate this pump is rated at which is approx 3500L / hr......Am I misunderstanding something here?