Bigger Pump ?

[billm]

Hi, The upstairs rads have always been alot cooler than the downstairs rads, I've balanced the whole house but they are still cooler, although its a small improvement.

The house is pretty big 4bed so these upstairs rads are alot further than the downstairs rads. The system is 100btu, 2 pipes, its about 20 years old and was flushed about 4 years ago - which didnt realy improve things - and the rads have thermo valves but to be honest they never kick in cos they dont get hot enough.

A local plumber advised last year to get a bigger pump. The one fitted is a Grundfoss 15/50.

What size of pump should I go for and will it improve the circulation and specifically the heat to these upstairs rads.

Can I de-gunk the system/pipes myself or does it need a to be done under pressure by a plumber ?

thanks for your suggestions

 

[D_Hailsham]

I've balanced the whole house but they are still cooler, although its a small improvement.

It's very unusual for a house to need a pump larger than a 15/50. So, before you spend money unnecessarily, we need to check other things out.

1. What boiler do you have?
2. What are the flow and return temps at the boiler?
3. Do you have a bypass?
4. What procedure do you follow when balancing the rads?

 

[PerryOne]

The 15/50 is a good pump, designed to lift water 15 meters or fifty feet.
It has three settings, which one are you using?
Water always takes the easy route, back to the pump.
So when you say you have tried balancing the radiators, what did you do?
As balancing involves closing the lock shield valve on the radiator closest to the boiler to push the water on to the next radiator, and so on.
When using Thermostatic valves balancing isn't really required as, as each radiator reaches it set temperature it closes and pushes the water on to the next cold radiator.
So, how hot is your boiler? On a scale of one to ten?

 

[ChrisR]

If the heating demand is anywhere near 100kBtu/hr, especially if it's with 22mm pipe, you don't stand Kylie's chance in hell of getting all the heat out from the boiler.
You need a 15/60 at least.
If any of the pipework to your "slow" rads is undersized a bit, then you'll have to throttle the better ones down to balance things, which will make the situation worse.

While you're doing your tests, make sure the valve to the HW cylinder is closed, and not "passing" at all. It's a much easier route for the water to take, unless that's balanced too, which it hardly ever is. Any fixed bypass will knobble the pressure too.

To anyone who thinks otherwise - do the sums.

 

[billm]

The boiler is a Glow worm Hideaway 100B - about 20 years old. I haven't got a clue what the input and output temperatures are. By bypass, I assume that would be the hall radiator which hasn't got a thermostatic valve on it - unless there's another pipe/valve somewhere. I think the boiler fires continually. It doesn't shut off and rest after an hour or so which would imply that the return water is still not hot enough for it to have a rest.

When I balanced the rads, I closed the valve (lock shield) on each rad about 1/2 way on those that were hot and left them open on the colder ones upstairs. I didn't check any bypass pipework or shutoff any hotwater/cylinder valve

And yes the pump looks like its on 22mm pipework. I didn't know the 15/50 had 3 settings so I can't check at the moment what it is set to. Do they make a big difference ?

I'm also thinking that I should flush the system again. I'm not sure the plumber did it right last time as he seemed to do it in an hour or so and I believe the stuff you put in has to circulate for a couple of days to really do its job bfore you let it out.

 

[patboyd]

The 15/50 is a good pump, designed to lift water 15 meters or fifty feet.


sorry, i am no expert, but i believe the 15/50 pump can lift / circulate water up to 5 metres in head, not 15.

as the grundfos 15 / 60 superselectric can circulate up to 6 metres of head.

where the names 15/50 and 15/60 come from i don't know though!!

 

[D_Hailsham]

I haven't got a clue what the input and output temperatures are.

OK. Have you got the boiler thermostat set to Max and does the return pipe feel cooler than the hot? If you can obtain/borrow a thermometer it would give a better idea. The difference should be 11°C (20°F)

By bypass, I assume that would be the hall radiator which hasn't got a thermostatic valve on it - unless there's another pipe/valve somewhere.

No, the hall rad is not the bypass. If you have one, it will be a pipe, immediately after the pump, which connects the flow to the return and has a valve on it to regulate the flow. Your boiler does not specify a bypass, so I doubt if you have one.

I think the boiler fires continually. It doesn't shut off and rest after an hour or so which would imply that the return water is still not hot enough for it to have a rest.

Boiler thermostats usually measure the flow temperature. So, if the boiler is running continuously it is never reaching temperature. Is the boiler set to Max temp?

When I balanced the rads, I closed the valve (lock shield) on each rad about 1/2 way on those that were hot and left them open on the colder ones upstairs.

Ah, that could be where you are going wrong

1. Set the system so only CH is on (no HW)
2. Open all lockshield and rad wheel valves and remove heads from TRVs.
3. Adjust the pump speed so you get approx 11°C drop at the boiler.
4. Shut down boiler and pump
5. Close all lockshield valves
6. Open lockshield valve on rad nearest the pump 1/4 turn and check the temp difference between flow and return pipes of the rad is 11°C.
7. If the diiference is too big, open the valve a fraction (no more than 1/4 turn)
8. Of the difference is too small, close the valve a fraction.
9. Repeat 6-8 on each rad in turn, moving away from the boiler
10. Check the boiler temperatures are OK and adjust pump speed if necessary
11. Replace and adjust TRVs to give desired room termperature

You may have to go round a couple of times to get everything correct - but don't aim for perfection. The important thing is to realise that it's only the first turn from closed on a lockshield valve which has any real effect.

I didn't know the 15/50 had 3 settings so I can't check at the moment what it is set to. Do they make a big difference?

Yes, if the pump is too fast it will be taking the water away faster than it can be heated, and vice versa. Your boiler needs a flow rate of 38 litres/second to deliver 29.3kW (100k BTU) with an 11°C temperature drop.

the plumber ... seemed to do it in an hour or so

So it wasn't a power flush then? If so, the flushing solution needs to circulate for at least two days and preferably as much as 4 weeks.

If you want to do it your self,

• Buy two cans of Sentinel X400 and two of X100.
• Drain and flush the system with plain water
• Refill with water, adding the X400
• Leave to circulate for several days (no more than 4 weeks)
• Drain and flush the system with plain water
• Refill with water, adding the X100

If any rads feel particularly cold at the bottom, they may be sludged up. You can help dislodge this by hitting the rad with a rubber hammer. You can also close down the other rads so the water only circulates through the problem ones. As a last resort you could remove the rad and flush through with a garden hose.

 

[D_Hailsham]

The 15/50 is a good pump, designed to lift water 15 meters or fifty feet.

sorry, i am no expert, but i believe the 15/50 pump can lift / circulate water up to 5 metres in head, not 15.

as the grundfos 15 / 60 superselectric can circulate up to 6 metres of head.

where the names 15/50 and 15/60 come from i don't know though!!

You are partly correct and PerryOne has got it completely wrong However the 50/60 does not refer to how high the pump can lift the water, but the pressure in the CH pipework due to friction. (5 metres ~ 0.5 bar or 50 kPa pressure)

The 15 refers to the diameter of the inlet and outlet ports of the pump and the 50 or 60 means 50 or 60 decimetres (5 or 6 metres). Why they use a 15mm port on a pump which is usually fitted to 22mm pipe is another mystery.

 

[billm]

Ah, that could be where you are going wrong

1. Set the system so only CH is on (no HW)
2. Open all lockshield and rad wheel valves and remove heads from TRVs.
3. Adjust the pump speed so you get approx 11°C drop at the boiler.
4. Shut down boiler and pump
5. Close all lockshield valves
6. Open lockshield valve on rad nearest the pump 1/4 turn and check the temp difference between flow and return pipes of the rad is 11°C.
7. If the diiference is too big, open the valve a fraction (no more than 1/4 turn)
8. Of the difference is too small, close the valve a fraction.
9. Repeat 6-8 on each rad in turn, moving away from the boiler
10. Check the boiler temperatures are OK and adjust pump speed if necessary
11. Replace and adjust TRVs to give desired room termperature

You may have to go round a couple of times to get everything correct - but don't aim for perfection. The important thing is to realise that it's only the first turn from closed on a lockshield valve which has any real effect.

Ah right, thanks for a very comprehensive reply. I will check everything this weekend, its not my house but a relatives so there's a bit of a delay while I try things out, but I'll get back to you when I've followed all your advice.

thanks again, much appreciated

 

[ChrisR]

Oh dear.
Comprehensive maybe, but wrong, wrong, wrong and wrong.

So it wasn't a power flush then? If so, the flushing solution needs to circulate for at least two days and preferably as much as 4 weeks.

Wrong.

Open all lockshield and rad wheel valves and remove heads from TRVs.
Adjust the pump speed so you get approx 11°C drop at the boiler.

Wrong. You probably won't get it.

needs a flow rate of 38 litres/second

Wrong again.
More like 0.63 l/s . At that rate a 15/50 will give you at max a couple of metres head for the pipework. Which in 22mm is enough for about 6 metres length. 3 metres flow + 3 metres return. Probably not enough for your house??

HAven't got time for a full answer to all this - suggest you do some more reading.

 

[billm]

Oh dear.
Comprehensive maybe, but wrong, wrong, wrong and wrong.

HAven't got time for a full answer to all this - suggest you do some more reading.

Chris, I posted the question on here looking for advice. If you are saying the above is wrong, what's your suggestions I should do to make it work better (apart from do some more reading) ?

thanks

 

[D_Hailsham]

So it wasn't a power flush then? If so, the flushing solution needs to circulate for at least two days and preferably as much as 4 weeks.

Wrong.

Sentinel X400 instructions say: Where systems are badly fouled, a longer period of circulation (e.g., up to 4 weeks) is recommended,

Open all lockshield and rad wheel valves and remove heads from TRVs.
Adjust the pump speed so you get approx 11°C drop at the boiler.

Wrong. You probably won't get it.

If you can't achieve the correct differential with all valves and lockshields open then your pump is undersized and you wont have any chance when valves are shut and the differential pressure across the pump increases.

needs a flow rate of 38 litres/second

Wrong again. More like 0.63 l/s .

Lapsus stylii. Should have typed 38 litres/ minute

 

[Agile]

If you can't achieve the correct differential with all valves and lockshields open then your pump is undersized and you wont have any chance when valves are shut and the differential pressure across the pump increases.

If the boiler is not cycling then it sounds as if the boiler output is insufficient for the rads.

The correct starting point is to measure the power output of the boiler and compare that with the heat output of the rads to ensure that they are matched.

Although a 15/60 would be the most appropriate pump for a non condensing system I would not have expected much diminution of performance with a 15/50 and if it was really unable to move enough heat at 30 kW then the boiler would be cycling !

Tony

 

[ChrisR]

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ChrisR wrote:
Quote:
So it wasn't a power flush then? If so, the flushing solution needs to circulate for at least two days and preferably as much as 4 weeks.

Wrong.

Sentinel X400 instructions say: Where systems are badly fouled, a longer period of circulation (e.g., up to 4 weeks) is recommended,

I know what the instructions on X400 say.
It doesn't apply to all Powerflushing. Your answer was wrong.

Quote:
Quote:
Open all lockshield and rad wheel valves and remove heads from TRVs.
Adjust the pump speed so you get approx 11°C drop at the boiler.
Wrong. You probably won't get it.

If you can't achieve the correct differential with all valves and lockshields open then your pump is undersized and you wont have any chance when valves are shut and the differential pressure across the pump increases.

And if he has a rad right next to the pump your "method" won't work, so there's two reasons why it's wrong.

Quote:
Quote:
needs a flow rate of 38 litres/second

Wrong again. More like 0.63 l/s .

Lapsus stylii. Should have typed 38 litres/ minute

No it wasn't just a typo. If you'd realised the consequences of what you wrote you'd have seen it was obviously wrong.

-----------

Chris, I posted the question on here looking for advice. If you are saying the above is wrong, what's your suggestions I should do to make it work better (apart from do some more reading) ?

Bill, unfortunately not many plumbers have unlimited time to give free advice!
You're getting a lot of rubbish which needed putting straight, then I had to do some WORK!
Change the pump yours is too small. I already told you that and I've given you reasons and figures.
You will than have one thing right. The old pump may be worn/blocked etc.

However, if, as is quite likely:
Your rads don't need a 100kBtu boiler.
Your pipework is undersized
You may not be correct about the boiler being on (firing) all the time
The boiler may be range rated (ie downwards)
Your system has sludge in it.........

then design advice goes out of the window.

 

[D_Hailsham]

The correct starting point is to measure the power output of the boiler and compare that with the heat output of the rads to ensure that they are matched.

One point which has not been considered is whether the boiler has been range rated. We have all assumed that the boiler is delivering the full 30kW. If it is, the flow and return pipe should really be 28mm, otherwise the water velocity would be too high. 22mm is only recommended up ~ 22kW. The OP also has not said what the boiler thermostat is set to.

More like 0.63 l/s . At that rate a 15/50 will give you at max a couple of metres head for the pipework. Which in 22mm is enough for about 6 metres length. 3 metres flow + 3 metres return.

A 22mm pipe has a resistance of ~0.1 metres per metre length. The 15/50 can handle a head of ~2m at 0.63 l/s which means about 20 metres of 22mm pipe. That does not take into account the 15mm pipework and the resistance of the radiators etc.

The Recommended Boiler Size Calculator will give a good indication of the size boiler need and the Stelrad Elite Catalogue can be used to estimate the output of the existing rads. This will tell you if the current boiler is correctly sized for the existing rads and whether the total rad output is adequate for the house.