HELP! Central heating pump knackered!

[Johntheo5]

That selectric graph above is, IMO, wrong, can't see it circulating 0.6LPS, 36LPH @ 3.0M, that shoud read m3/hr, so 0.6m3/hr, 10.0LPM. I think the 95/100W super selectric actually circulates 10.0LPM @ nearly 4.0M, however we'll use the lower head of 3.0M.

If we assume that your system requires 3.0M to circulate 10.0LPM, then, because flow is proportional to the sqroot of Head, the UPS3 will circulate [email protected] (speed1), 13.17LPM@ 5.2M (speed2) & [email protected] (speed3) . Unfortunately, Grundfos's PP (propoptionl pressure) settings are far too low, running that pump on PP2(3.5M) will only result in a flowrate of [email protected], the Evosta3 (or the Wilo with its infinite CP&PPsettings) would give [email protected] since its PP2 head is 4.5M.

What mode/setting are you using just now?.

 

[Avocet]

That selectric graph above is, IMO, wrong, can't see it circulating 0.6LPS, 36LPH @ 3.0M, that shoud read m3/hr, so 0.6m3/hr, 10.0LPM. I think the 95/100W super selectric actually circulates 10.0LPM @ nearly 4.0M, however we'll use the lower head of 3.0M.

If we assume that your system requires 3.0M to circulate 10.0LPM, then, because flow is proportional to the sqroot of Head, the UPS3 will circulate [email protected] (speed1), 13.17LPM@ 5.2M (speed2) & [email protected] (speed3) . Unfortunately, Grundfos's PP (propoptionl pressure) settings are far too low, running that pump on PP2(3.5M) will only result in a flowrate of [email protected], the Evosta3 (or the Wilo with its infinite CP&PPsettings) would give [email protected] since its PP2 head is 4.5M.

What mode/setting are you using just now?.

Isn't 0.6 LPS 36 litres per minute though? I used 0.6 x 60 x 60 = 21600 LPH and then divided that by 1000 to get cubic metres (so 2.16 cubic metres per hour).

Right now, it's on the manual fixed highest speed. It said to do that initially, to make sure all the air pockets were out. I've been round the radiators today, and they all seem air-free, so I was just about to try one of the "variable" settings.

 

[Johntheo5]

Yeah, should have said LPM, but no way is that possible with that pump, I would suggest trying CP1 at a constant 3M which should be close enough to what you were getting with the Selectric, if too low try CC1 at 4.5M if CP1 is OK you can allways then try PP2 and see how you get on.
Do you have TRV's.

 

[Avocet]

Yeah, should have said LPM, but no way is that possible with that pump, I would suggest trying CP1 at a constant 3M which should be close enough to what you were getting with the Selectric, if too low try CC1 at 4.5M if CP1 is OK you can allways then try PP2 and see how you get on.
Do you have TRV's.

Excellent, thanks! And yes, we have TRVs on all the radiators.

 

[fixitflav]

25mm refers to the pump port(s) diameter, the connections are definitely OK, 1 1/2 ins, 2ins across the flats. When I installed mine 5 years ago, it replaced a old Salmson and I used the original isolating valves.

But the data sheet doesn't say 25mm, it says 1" BSP, which is a nominal pipe size. I'm sure it's not a problem in practice, we all know it's 1½" BSP.

 

[oilhead]

If you turn down the speed on a combi like yours you may adversly affect the hot water temperature. Combi's usually run on top speed.

 

[Johntheo5]

A good point allright, so a PP setting is out but I would think that CP2 at 4.6M should be fine as the selectric was scarcely producing that head at its full speed, for interst, it would be good to try a minimum CP1 setting, if head (3.0M) not sufficient then CP2 (4.6M) should do the job and certainly CC2 at 5.2M, otherwise PHEX may be getting blocked?, its only a few button presses.

 

[Avocet]

A good point allright, so a PP setting is out but I would think that CP2 at 4.6M should be fine as the selectric was scarcely producing that head at its full speed, for interst, it would be good to try a minimum CP1 setting, if head (3.0M) not sufficient then CP2 (4.6M) should do the job and certainly CC2 at 5.2M, otherwise PHEX may be getting blocked?, its only a few button presses.

Yeah, I'll give it a go. Hot water is also flaky because the diverter valve doesn't work properly. Basically, this is a 30 year old obsolete boiler nearing the end of its days!

 

[Avocet]

Just an update guys, after having run it for the best part of a month. I've tried it on the second "automatic" setting, and on colder days, it struggles to keep the upstairs radiators fully hot. I tried opening the lockshield valves a bit more, but it doesn't seem to make a huge amount of difference. I think that on very cold days, it's probably best if I keep it on its manual third speed.

 

[Johntheo5]

Just an update guys, after having run it for the best part of a month. I've tried it on the second "automatic" setting, and on colder days, it struggles to keep the upstairs radiators fully hot. I tried opening the lockshield valves a bit more, but it doesn't seem to make a huge amount of difference. I think that on very cold days, it's probably best if I keep it on its manual third speed.

What's the second automatic setting?, do you mean PP2?, (UPS3??), speed III, at 6.4M is more than double the head "normally" required for most systems, the PP settings on the UPS3 are pretty poor, far too low, I'd be surprised if speed II at 5.2M (or even speed I at 4.2M) didn't circulate enough to the upstairs rads.

 

[Avocet]

What's the second automatic setting?, do you mean PP2?, (UPS3??), speed III, at 6.4M is more than double the head "normally" required for most systems, the PP settings on the UPS3 are pretty poor, far too low, I'd be surprised if speed II at 5.2M (or even speed I at 4.2M) didn't circulate enough to the upstairs rads.

Yes, I was a bit surprised. It's "Proportional Pressure II" mode. However, looking at the graph, that's not able to cope with a great deal of head?

It also says that it's not suitable for systems that include an automatic bypass valve:

...but I don't know if mine has one or not?

 

[Johntheo5]

Oil fired boilers generally don't require a ABV as the boiler HEX will soak up any residual heat when any heat demand suddenly stops, my 20kw Firebird has a 21L HEX, the temp rises from 65C to ~ 90C after shutdown but the Hi limit stat doesn't operate until 110C/113C so no problem and neither should yours as you also have a primary heat store (combi).

I require 3.6M head to circulate 15LPM through 10rads with (8) all TRVs fully open, my 6M Wilo Yonos Pico has almost infinite settings (0.1M steps) in both PP & CP modes, I have it set to 4.6M (PP mode) which gives me the required 3.6M/15LPM, but reduces the head as the TRVs close in, no noise & a little energy saving, from ~ 22W to 12/14W depending on heat demand.
If had a UPS3 pump then because of its lowish PP head then it should circulate 12LPM @ 2.3M, 12LPM isn't bad, the problem is that the low head just doesn't circulate proportionally through the rads without more balancing, a pain.

How was the DHW performance from the boiler when running in PP mode??

 

[Avocet]

Oil fired boilers generally don't require a ABV as the boiler HEX will soak up any residual heat when any heat demand suddenly stops, my 20kw Firebird has a 21L HEX, the temp rises from 65C to ~ 90C after shutdown but the Hi limit stat doesn't operate until 110C/113C so no problem and neither should yours as you also have a primary heat store (combi).

I require 3.6M head to circulate 15LPM through 10rads with (8) all TRVs fully open, my 6M Wilo Yonos Pico has almost infinite settings (0.1M steps) in both PP & CP modes, I have it set to 4.6M (PP mode) which gives me the required 3.6M/15LPM, but reduces the head as the TRVs close in, no noise & a little energy saving, from ~ 22W to 12/14W depending on heat demand.
If had a UPS3 pump then because of its lowish PP head then it should circulate 12LPM @ 2.3M, 12LPM isn't bad, the problem is that the low head just doesn't circulate proportionally through the rads without more balancing, a pain.

How was the DHW performance from the boiler when running in PP mode??

Thanks for that reply. I must admit, I'm struggling with some of the abbreviations, though!

"HEX" = "heat exchanger"?
"DHW" = ???

 

[thomp1983]

Your right with hex, dhw is generally domestic hot water

 

[Avocet]

Thanks both,

DHW isn't a good metric to choose, as my diverter valve is knackered and obsolete. I just move it manually if we want a bath (which is rare), and the showers are cold-fed electric anyway. There's always about a gallon available for washing-up if needs be.