Central Heating Pump Speed

[gmtsteve]

I have searched the forum for an answer, but found conflicting advice. Since the searches were for bigger systems than mine, I thought I would ask the question again.

I have a smallish system of only five radiators in a small semi, with micro bore pipes. The main room has a room thermostat and no thermo on the rad, all the other rads (except the bathroom) have thermos on them. The boiler is quite small ( a Potterton Suprima).

I have the pump (circulator) speed set to 1-the lowest position and all seems well. With the recent very cold weather though, I can't help thinking it's not as warm as it should be. All the rads are very hot to touch and the boiler doesn't make any funny noises. Another post I read did say that at the lowest setting, you wouldn't get enough energy out of the boiler. Then again, another few posts say that the lowest setting that the system works at is the right setting. My understanding (very limited as it is) is that if the rads are hot, then moving the water faster won't get them any hotter.
Can someone help me find the proper, most efficient setting for my Grundfos Selectric circulator pump please?

 

[kevindgas]

sounds like the rads are undersized rather than the boiler being at fault

 

[Happyplumber]

I have to agree with kevin,if the rads are hot then obviously making the pump going faster will make no difference

The rads seem to be undersized and also check the insulation and try to increase it where possible

 

[gmtsteve]

Sorry, I might not have worded things clearly enough. I should have said, the house is warm, I'm just worried in case I'm not getting as much efficiency as I should.
When I moved in 3 yrs ago, I thought the CH was very noisy, but put it down to being in a modern semi, after a much older, bigger house. Thinner walls etc. Then, when the system was being serviced as part of an annual service contract, I mentioned that one radiator in particular needed bleeding regularly. The engineer reckoned cavitation from too high a pump speed might be to blame and turned it down from 3 to 2. In the following days, I noticed that this had also dropped the noise too, so I tried it on the lowest setting 1 and as I said, everything seemed fine and certainly much, much quieter. Now the really cold weather is here though, I'm just concerned that the lowest setting might not be getting the most out of the system.
So if on the lowest setting, the rads are hot, the boiler doesn't make funny noises, then that is the correct setting?

ps. The rad I mentioned still needs regular bleeding even on setting 1. The pump seems fitted upside down too since the label is upside down.

 

[theheatinghelper]

(most of the time) the pump pulls heat away from the boiler and pushes it into the system there will be a small arrow on the back of the pump to say what way it is going. try turning the pump up, whats the worst that can happen? it pushes over the open vent ? the way i see it is if there are 3 settings on a pump why cant u use 3 or the settings, click it on the second setting and see how it goes u can always turn it back to one again !!! good luck !

 

[Nige F]

Rad constantly needs bleeding = design fault in pipework or drawing air in on suction side of pump - 5 rads possibly undersized - microbore -..could have been bunged in on a budget