Just trying to make my heating system run more efficiently, the heating return temp is only a couple of degres less than the feed, the pump speed is set a 3, can i lower the speed? the system consists of 10 rads and 30m2 unfloor heating.
Combi Condensing boiler pump speed
- Thread starter landy6
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no its designed to run on three ,to shift water through the boiler at a certain rate on hot water
cant say, its a job that would need looking at to see the system
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Which make/model/size boiler do you have?
What is the total heat loss of your house? Use Boiler Size Calculator to find out.
What is the total heat loss of your house? Use Boiler Size Calculator to find out.
What is your boiler? Often the boiler allows you to turn down the pump speed for heating but still knows to use it at full power for water. Or not, depending on the boiler. Setting "3" on a typical pump is way high for most houses, but with UFH included in the mix who knows what your needs might be. Do you have a separate pump for the underfloor section?
Is there an automatic by pass on the system? It will come immediately after the heating pump and is on a pipe connecting flow to return?
The boiler is OK for the heat loss - possibly oversized. Do you know what the output is set to - it can be between 18 and 25kW?
Did the installer check you cold water flow rate before specifying the size of boiler? A 25kW boiler will raise the temperature about 35degC at a flow rate of 10 litres/min. If the flow rate is higher the temperature rise will be lower and vice versa.
it has a 0.55 nozle fitted so is running at 21.5kw, it also has 16.8 l/min at 66.1'c. If i slow down the pump to give the rads and ufh chance to release the heat will this have i big impact on my hot water? There isn't a bypass fitted on any of the pipes fitted to the boiler-unless there is one built into the boiler itself-before the feed/return connects to the house. is this an issue?
Is that the hot water flow rate and temperature? I did ask if the installer had checked the cold water flow rate at the kitchen tap.
It may not be, Worcester only say you need one if TRVs are fitted. The check list in the back of the Installation Manual should say if it has been fitted or if it is not necessary.
You should not change the pump speed setting.
What number do you have the heating temperature set to on the boiler?
Have you tried varying the temperature to see what effect it has?
Do you have a sealed or open-vent system? If it's sealed, what is the pressure when cold and when hot?
Have you tried varying the temperature to see what effect it has?
Do you have a sealed or open-vent system? If it's sealed, what is the pressure when cold and when hot?
Its a sealed system, running at 1.5bar cold and about 1.7 hot, i have turned it done in the past but the rads don't seem to put of much heat then, its currnetly running at 3.5 (6 is max) maybe just slogging a dead horse, should maybe just leave it be and just keep filling up with oil more often.
As far as I can tell, you need to limit the temperature rise across the boiler when it is running at full chat warming up. An infra-red thermometer and some black PVC tape on the flow and return is one way to measure it. If the maximum temperature rise is much less than the boiler spec, there might be scope to reduce the flow rate.
Unfortunately, maximum heating efficiency isn't always just about getting the boiler condensing. For example, if your pipe work runs outside the 'heated envelope' and is poorly insulated, dropping the water temperature and running the heat for longer can increase losses from these pipes. As the temperature is lowered, the heat lost from the pipes increases as a proportion of the useful heat. To demonstrate, let's say that the temperature under the floor is 0ºC and the room temperature is 20ºC. At a boiler flow temperature of 80ºC, the excess temperatures are in the ratio of 80:60 or 4:3 (1.33). If the flow temperature is dropped to 60ºC, the excess temperatures are in the ratio of 60:40 or 3:2 (1.5). Given that you need the same heat in the house, 12.5% more heat will be lost under the floor because the pipes will be less hot but for much more of the time. Obviously, the pipes under the floor should get insulated so the increase is 12.5% of not a lot, but that can be very disruptive.
If you get an infra-red thermometer, check the boiler flow temperature and various (ground floor) radiator flow and return temperatures. Ideally, the temperature drop in the pipes between the boiler and a radiator should be small compared to the temperature drop across the radiator. If you have an old system, you might be disappointed.
Unfortunately, maximum heating efficiency isn't always just about getting the boiler condensing. For example, if your pipe work runs outside the 'heated envelope' and is poorly insulated, dropping the water temperature and running the heat for longer can increase losses from these pipes. As the temperature is lowered, the heat lost from the pipes increases as a proportion of the useful heat. To demonstrate, let's say that the temperature under the floor is 0ºC and the room temperature is 20ºC. At a boiler flow temperature of 80ºC, the excess temperatures are in the ratio of 80:60 or 4:3 (1.33). If the flow temperature is dropped to 60ºC, the excess temperatures are in the ratio of 60:40 or 3:2 (1.5). Given that you need the same heat in the house, 12.5% more heat will be lost under the floor because the pipes will be less hot but for much more of the time. Obviously, the pipes under the floor should get insulated so the increase is 12.5% of not a lot, but that can be very disruptive.
If you get an infra-red thermometer, check the boiler flow temperature and various (ground floor) radiator flow and return temperatures. Ideally, the temperature drop in the pipes between the boiler and a radiator should be small compared to the temperature drop across the radiator. If you have an old system, you might be disappointed.
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