A couple of questions

[Bas]

I have a standard vented heating setup, Boiler is Apollo.
Question 1... how can I tell if my pump is worn or becoming less efficient? It still works but the rads at the far end of the system don't get as hot as they did unless I turn off others in that circuit? (its at least 10 yrs old)

Q2 After the pump on the flow side is a 15mm pipe with a valve between the boiler flow and return. What is this for, and should it be open or closed. Answers much appreciated

 

[ChrisR]

Q2 - it's a "bypass". Somewhere for the boiler to circulate hat water if all rad valves are shut. If yuo have a 3 port valv3 you don't really need one cos the 3 port will always be open somewhere. Theey were used on Iron boilers to keep the return temp up, to avoid condensation in the boler. Yours is copper. ALSO it reduces the head of water available to the system though, to affect question 1

Q1 Short answer is that you can't. They do wear their impellers - and sometimes go slow. Is it on full speed? That shouldn't be necessary on a smallish system. Try Balancing your system (closing the lockshields on the hotter rads a bit). Sludge is always a probability on an old system, which slows circulation. It makes the bottom of rads cool.

 

[oilman]

Question 1: The radiators are more likely to be giving out less heat because of sludge in the system, than the pump being a problem. First thing to do is to cleathe system. This is a no-loss exercise, as it may fix the problem completely, or it may at least improve matters.

Question 2: the pipe is a bypass pipe, and is used to allow some flow if all of the radiator valves shut down together. The valve should be one of these

details here . Using a gate valve etc is a cheap and unsatisfactory bodge as you can't stop the flow when it's not needed. These valves have the function of keeping the return temperature up, and so make another joke of condensing boilers.

 

[Bas]

Thanks (again) for some very informative answers, I'll give the affected radiators a flush out this weekend! I live in a threee story house and they are on the ground floor and fed by small bore pipe!

I'm not completely sure what Chris meant by "ALSO it reduces the head of water available to the system though, to affect question 1" but as its a gate valve now I will replace it with a the differential pressure valve when the system is drained. I have TRV's but at least one is always set to fully open.

 

[ChrisR]

I'm not completely sure what Chris meant by "ALSO it reduces the head of water available to the system though, to affect question 1"

The greater the flow through the system, the lower the pump head (pressure) available. Therefore a simple valve type bypass lowers the available pressure. You could try closing the valve to see what it does to your "slow" rads.

What cobtrols do you have on the system? If 2 x 2 port valves, you can't use a downstream rad as a bypass.

 

[Bas]

Controls are TRV's, programable room stat and a three port mid posn valve. I'll close the bypass and see what happens. Thanks again for your time

 

[ChrisR]

Replace the trv on the rad adjacent rad to the radstat with a lockshield one, turned down to give the trv's a chance to control the rooms. Then you can shut the bypass.

 

[Bas]

Replace the trv on the rad adjacent rad to the radstat with a lockshield one, quote]
Sorry Chris I don't understand