Central heating pump help needed

[amah]

My house initially had 11 radiators and all of them worked very well. Now 4 extra radiators have been added due to extension built to the house. The problem is that these 4 new radiators are not heating up at the same time, only two of them are actually heating up. This means I have to turn the thermostat valve off on 2 to get the other 2 to heat properly. I can choose which of the 2 radiators heat up. The pump is British Gas Multi Head G P/N 595061809 PC 0841. Do I need a faster pump, something like Grundfos UPS2 15-50/60?

 

[D_Hailsham]

How are the new rads connected into the existing system? Were they separately connected to the main (22mm) pipes or were they piggy-backed off the feed pipes to existing rads?

Did the installer rebalance the system?

 

[amah]

Thanks for your reply.
The new radiators are connected to the existing upstairs circuit.

The installer has tried to rebalance the system but would like to know if pump with faster flow would help.

I think Grundfos UPS2 15-50/60 has faster flow then my existing pump (British Gas Multi Head G P/N 595061809 PC 0841)

 

[oilboffin]

Get a pump with a good head go round the system Turn all lock shields off then open them one turn run heating go round feel rads if there's a really hot rad turn lock shield down half a turn that should
balance the system.Bob

 

[D_Hailsham]

The installer has tried to rebalance the system but would like to know if pump with faster flow would help.

The fact that you can get two rads to work but not all four shows that it's a balancing problem.

A competent installer should know that it's not a case of getting a faster flow but getting the correct flow. This is achieved by setting the temperature differential across each radiator to the appropriate value using the lockshield valve. (About 11C for old non-condensing boilers, and up to 20C for modern condensing boilers.) The flow through a 1kW radiator is 1.3 litres per minute for an 11C difference, and 0.72 lpm for a 20C difference; no exactly fast. The flow is proportional to the kW of the rad, so a 2kW rad will need twice the flow of a 1kW rad.

Post details of your boiler (make and exact model inc kW rating) and someone will tell you the correct temperature to use.

 

[amah]

Get a pump with a good head go round the system Turn all lock shields off then open them one turn run heating go round feel rads if there's a really hot rad turn lock shield down half a turn that should
balance the system.Bob

Which pump with a good head do you recommend as a replacement for British Gas Multi Head G P/N 595061809 PC 0841?

 

[amah]

The fact that you can get two rads to work but not all four shows that it's a balancing problem.

Post details of your boiler (make and exact model inc kW rating) and someone will tell you the correct temperature to use.

My boiler is Potterton Promax He. I don't know the kw rating.

 

[D_Hailsham]

My boiler is Potterton Promax He. I don't know the kw rating.

I don't need the kW rating; Promax HE is enough.

Your boiler is designed for a 20C drop between flow and return connections at the boiler. If you try to set it up with a 10-11C difference you will run into trouble as the resistance of the heat exchanger will increase considerably (about 4 times) due to the faster flow rate. This will require a more powerful pump - as you have found.

Your pump has a 6 metre head, on the highest setting, so there's no need to change it. In any case you should find it works correctly on a lower setting if the system is balanced for a temperature nearer 20C.

Balancing Procedure

Ideally, you need some means of measuring the flow and return temperatures at each radiator. However, you can get reasonable results using your hands.

1. Remove all TRV heads; set all wheel valves to fully open
2. Close all lockshield valves, then open half a turn
3. Set programmer so only heating is working
   
4. Set pump to middle speed
5. Turn heating on and allow boiler to heat up. (Set room stat to a higher temperature so it doesn't turn boiler on and off.)
6. Check, by feel, the temperature difference at each rad and identify the rad with the smallest difference, i.e hottest return.
7. Close the LS valve by 1/12 turn and wait 10 minutes for system to settle down.
8. Repeat from 6 until all rads have approximately the same drop
9. If you find that some LS valves are virtually closed, set the pump to the lowest speed and all LS valves open half a turn. Then start again from 6
   
10. Replace all TRV heads and set to required temperature
11. Set room stat to required temperature

You may find that, in some cases, the TRV is on the return (cooler) side. This doesn't matter; you still adjust the LS valve to alter the temperature drop.

 

[oilboffin]

Grundfoss pumps rule in my book great pumps I think you can get a 7metre head pump which will belt the water round and when alls well turn it down.Bob

 

[Terrywookfit]

Who fooks around measuring rad temp ?

If it's hot the punter is happy !!

 

[oilboffin]

Yup.Bob

 

[amah]

Any idea why I am getting temperature difference (drop) of only around 5 degrees? Is there a problem with the pump?

 

[abbadon]

That means likely flow is too fast.... Water isn't getting time to release its energy fully to your room. Read further up this thread. This will result in inefficient boiler operation I think?

 

[D_Hailsham]

Any idea why I am getting temperature difference (drop) of only around 5 degrees? Is there a problem with the pump?

1. Where are you measuring the temperatures, at the boiler or a radiator?

2. What are the actual temperatures?

That means likely flow is too fast.... Water isn't getting time to release its energy fully to your room. Read further up this thread. This will result in inefficient boiler operation I think?

Yes, the flow is too fast; but that doesn't mean the energy is not being released. The formula for energy produced is:

kW = Flow x Temperature drop x 4.18 (Specific heat of water).

So a flow of 10 litres/ minute with a 10C drop produces the same amount of energy as a 20 litre flow and a 5C drop.

The output from a radiator does depend on the actual temperatures and not just the differential, which is the reason for the question above. But, provided the mean temperature is the same, there is very little difference between a delta of 5C, 10C or 20C. A 1 kW rad, measured at 75/65/20 (mean = 70C), produces 987W at 80/60/20 (mean still 70C). It's only when the mean drops that output drops significantly. For example the "1kW" will only produce 868W at 70/60 (mean 65) and 619W at 60/50 (mean 55).

 

[abbadon]

1. Where are you measuring the temperatures, at the boiler or a radiator?

2. What are the actual temperatures?


Yes, the flow is too fast; but that doesn't mean the energy is not being released. The formula for energy produced is:

kW = Flow x Temperature drop x 4.18 (Specific heat of water).

So a flow of 10 litres/ minute with a 10C drop produces the same amount of energy as a 20 litre flow and a 5C drop.

The output from a radiator does depend on the actual temperatures and not just the differential, which is the reason for the question above. But, provided the mean temperature is the same, there is very little difference between a delta of 5C, 10C or 20C. A 1 kW rad, measured at 75/65/20 (mean = 70C), produces 987W at 80/60/20 (mean still 70C). It's only when the mean drops that output drops significantly. For example the "1kW" will only produce 868W at 70/60 (mean 65) and 619W at 60/50 (mean 55).

you missed my intent, I agree that heat out of the radiator will be the same, we cant beat physics but the return temperature to the boiler will be too high, which was the OP's concern. so the delta T is too low, and too much energy is being returned with the water to the boiler, and as such it may not operate at the most efficient level?