House too long

[busterwebb]

Sorry to ask this question again but i didn't get any replies first time.

My house is 100 feet long with an oil fired boiler at one end (28kW) and 24 radiators. There's a single grundfos pump on the return leg to the boiler. Gravity fed, un pressurised, doesn't heat the hot water.

The problem is that the rads at the far end of the house are luke warm at the top and cold on the bottom. It has been cleaned with x800 but not power flushed.

Help - what can I do?

 

[buck51]

Anything you want to its your house ,but I would try power flush first

 

[NiallEvans87]

How long have you noticed this problem, since you moved into the property or has it gradually got worse?

What size is the pump and has it been replaced recently?

What speed is the pump set to?

How hot to the touch would you say the radiators are closest to the heat source?

Is there a motorised valve/3 port valve?

Is the hot water unusually hot?

Is there a manual or automatic bypass on the system?

What is the boiler stat set to?

 

[busterwebb]

Thanks for taking an interest,
1. I bought the house three years ago (a barn conversion) and the previous owner said the heating has never worked properly. Flushing with x800 made it slightly better, but marginal improvement.
2. The pump is a grundfos 15-50 and its never been replaced. Hums along nicely though.
3. It's set to maximum speed (3)
4. Closest to the heat source the radiators are hot to touch top and bottom. In the middle of the house they are cooler on the bottom, and at the the far end of the house warm on the top and cold on the bottom.
5. There are no motorised valves. its a simple send and return loop with all 24 radiators hanging off the loop on 10mm microbore. The loop starts at 28mm, then 22mm then 15mm.
6. The hot water is on a completely different circuit fed from an aga back boiler.
7. There's no bypass circuits that I can see but all 24 rads have trvs.
8. The boiler stat is set to a mid-way position - i'm guessing the water is about 65 degrees. it's an elderly Potterton statesman 28kW oil boiler an I've had to strip down the oil pump every winter to keep it going. Going to have to bite the bullet and replace the boiler soon.

I wondered whether i could fit a booster pump half way along the loop. But i can't see what would stop the water exiting the pump, going round the 'upstream' radiators the wrong way and creating a loop of cold water.

 

[AdrianUK]

Has the system ever been balanced?

Have a look at the locksheild valves (the ones with the cover instead of a knob which turns the valve shaft).... are they all fully open? If they are then its probable that the system has never been balanced properly.... this could well be the route cause of the problem.

By balancing the system, you throttle down the flow rate through those radiators closest to the boiler to alllow more hot water to reach the lat radiators on the run. To do this you need a couple of pipe thermometers and some time. Its an iterative process and takes sevral hours/days to do properly but will be worth it.

Adrian

 

[Nige F]

2. The pump is a grundfos 15-50 and its never been replaced. Hums along nicely though.

.

Replace it with a 15 / 60

 

[NiallEvans87]

+1 for balancing and putting a 15/60 grundfos. There's a start for you, you should see a noticeable difference in the heat to the furthest rads.

 

[Onetap]

In the middle of the house they are cooler on the bottom, and at the the far end of the house warm on the top and cold on the bottom.

That could be a symptom of sludge (corrosion products) in the radiator, hence the suggestion of power flushing.
The corrosion would only happen if oxygen was getting into the system.
You’re not certain that there is a sludge problem; I’d suggest disconnecting and taking one or two of the affected radiators outside and flushing them out with a hose to see what comes out and whether they are improved by the treatment.

If there is a sludge problem, I’d suggest checking the pump/OV/CF arrangement, possibly power flushing and installing a magnaclean or similar device to start cleaning the system up before you fit a new boiler.

The radiators should all get uniformly hot, if the system is balanced correctly. The furthest (least favoured) ones being cooler suggests it needs balancing AND/OR a partial blockage with sludge.

I wondered whether i could fit a booster pump half way along the loop.

I wouldn’t. One pump should be capable of dealing with this system, albeit maybe a bigger pump.
100 feet isn’t much, providing the pipes and pump have been sized correctly to ensure they are capable of providing the required flow rate.

There's a single grundfos pump on the return leg to the boiler.

IMHO, it would be better on the flow, pumping away from the boiler AND the cold feed (CF) and open vent (OV) connections. The existing arrangement would probably make it more likely that air could get drawn into the system; see above re sludge.

If the boiler has a manual-reset high-limit thermostat, I’d consider converting it to a sealed system to reduce the possibility of air being drawn in.

Where are the OV and CF connections from the feed & expansion cistern, in relation to the boiler?

Is the ‘loop’ in a floor void or ceiling void (air locks?).
Is it insulated?
Are all the rads on the ground floor?
Are there any leaks (F&E tank level drops when heating off and water fill isolated)?
Check the F&E tank is adequate (it doesn’t overflow when the system is hot).
Check the F&R connections to the boiler and thermostat location conform to the installation instructions (http://www.acwilgar.co.uk/Boiler-Manual-PDF/Potterton/Potterton_Statesman_Kitchen_Install_Guide%204.pdf ) .

The boiler stat is set to a mid-way position - i'm guessing the water is about 65 degrees.

Possibly too low; if the return temperature is regularly below 55degC, it will cause condensation in, and corrosion of, the boiler on the flue side.
The recommendation in the manual was to run the boiler near the maximum, ISTR.

 

[busterwebb]

Thanks for your various bits of advice.
I'll try balancing the radiators as AdrianUK advises, but every radiator has got a TRV, so I don't really understand what is added by balancing. But I'll give it a go.
I might as well up-gun the pump to a 15/60 - the extra flow rate can't do any harm.
Sludge could be a problem. May be worth paying somebody to do a power flush. When I cleaned the system with x400 recently I disconnected all 12 downstairs rads and drained them down, but didn't take them off the wall and flush them through. Maybe I should have done.
The overflow to the header tank (on the hot side) and the cold feed (on the cold side) tee into the send and return pipes about 50 feet from the boiler. Haven't spotted any leaks.
I'll try running the boiler hotter - it's easy to try.
And when I replace the boiler I'll go for a sealed system!
Anyway I'll try all these steps and report back.

 

[John506]

The water will only flow through the TRV as fast as the lockshield will allow it to, not the other way round

 

[Onetap]

The overflow to the header tank (on the hot side) and the cold feed (on the cold side) tee into the send and return pipes about 50 feet from the boiler.

That might be a problem.

The cold feed is on the suction side of the pump and the open vent is on the delivery side. There will be a pressure/head difference between those two points. If that head difference is more that the height difference of the OV above the expansion tank surface level, water will flow down the cold feed and up the open vent (pumping over). That will introduce air, causing corrosion and sludge.

The F&E tank should not get hot whilst the heating is on; if it does, there's a problem.

I suggested converting to a sealed system now for that reason, to stop any more crud forming that will clog up a new boiler (although it may not have much effect on the existing one).

Fitting a bigger pump without first resolving the corrosion problems (if any) will make it worse.

 

[doitall]

. There are no motorised valves. its a simple send and return loop with all 24 radiators hanging off the loop on 10mm microbore. The loop starts at 28mm, then 22mm then 15mm.

If you are sayings it's a one pipe system then I doubt it will ever work unless you re-pipe it.

Can you post a simple drawing showing the pipework.

 

[busterwebb]

I'll go up into the loft to see if the header tank gets hot - from memory I think it does. So onetap may be right and this is where the pressure is going.
Damn, I've just ordered a 15/60 pump.
Doitall, its not a one pipe system. There's send and return mains and each radiator is 10mm microbore fed to and from the send and return via 2 tees.

 

[doitall]

Blockage in the 10mm returns then.

Disconnect one rad and see whether you can draw a bucket or two of water from each pipe

it's probably undersized as well but need the info for that road.

 

[Agile]

Thanks for your various bits of advice.

I'll try balancing the radiators as AdrianUK advises, but every radiator has got a TRV, so I don't really understand what is added by balancing. But I'll give it a go.

Anyway I'll try all these steps and report back.

Just because you dont understand does not mean that its not required!

My advice would be to close each lockshield valve and then open it by JUST one full turn as a starting point.

Then see what effect that has. Its quite possible thats all you would need to do!

I agree that increasing the flow temp to about 70 C or 75 C would be better.

Tony Glazier