Inadequate Circulator Pump?

[John.g]

Yes, but those readings are all indicative of practically no circulation, if the pump discharge valve was closed fully, the readings would/should be the same, if I shut the discharge valve on my Wilo smart pump, the power readings will be exactly as its pump curves show for each different mode&setting at zero flow rates.

 

[ShaunCorbs]

Not really 33w on 3 on a pump 10 ish years old is moving / circulating and op says the system is working but the furthest away rads don’t fully heat / trouble balancing

 

[John.g]

Hard to disagree with that as 33W does seem very high for zero flow. Mine is 24W at zero flow, just tested it there now by shutting its discharge valve and its exactly as shown on its pump curve.
If the Alpha is re installed then quite simple to check it out by just shutting the discharge valve fully for 5/10 secs.

 

[JC22024]

Not really 33w on 3 on a pump 10 ish years old is moving / circulating and op says the system is working but the furthest away rads don’t fully heat / trouble balancing

OK so no change with the Wilo pump.

To explain this fully:

I have lived here since a child. Now 35. House has always been cold but I've done major upgrades to Building fabric in recent decade.

Heating always worked largely OK but also some rads were off always and never checked out. Pipes are 28mm on GF, 22mm on FF and 15mm to all rads no less than that.

House was renovated & extended over the years a couple of times in 80s.

Boiler is on one side of house so it has a job getting around all rads and back to boiler.

If I balance rads by feel only I get them all working on GF largest zone except furtherest away. If I turn others off then the furtherest one will come on hot.

Problem is even when the first floor small zone is on, when I balance first 2 rads accurately with thermometer to 11 degree drop, they feel toasty but then the other rads drop dead.

I do still believe the house simply requires a larger output circulator. This problem has existed for years and the new boiler is cranking out the heat but getting nowhere. I think for these purposes the Trident 180mm pump is worth a trial at least. If it proves the theory and I can balance rads properly and not lose heat / flow then can invest in a higher quality pump for long term use. Probably talking light commercial circulator here which I think the Trident may be albeit a cheap one.

 

[JC22024]

Sorry for poor quality but here is ground floor plan as example. Boiler is on far right wall.

It is back left bedroom that won't get hot when rads are balanced by feel only. Furtherest from boiler room

 

[JC22024]

OK better plan attached. (A bedroom single rad is removed at present)

Colour coded locations of rads on this Ground Floor. First floor is smaller on plan as it is a 1.5 storey house.

 

[ShaunCorbs]

Tbh my rule of thumb (engineers) 14-30 rads 25-80 under 15-60

 

[JC22024]

Tbh my rule of thumb (engineers) 14-30 rads 25-80 under 15-60

Thanks for that, am I right in thinking those figures may relate to

25mm inlet
80mm pump vane?

If so yes that would make sense as old units are 15mm inlet and 60mm vanes

 

[John.g]

GF only.
Does the boiler start to cycle a few minutes after a cold startup in the morning or does it run continuously for say 25/35 minutes before cycling?.

You have 28mm on the GF so a flowrate of 20LPM assuming 50M of pipework will require ~ 1M pump head, add another 1M for loss across rads etc then total head required = 2M so assuming no sludge in the system it should be no big deal to get sufficient circulation at least on the ground floor.
U/stairs with 22mm piping will require 3.4M to overcome pipe losses at 20LPM and 50M of piping, add another 1m across rads and total head required is 4.4M so a bigger problem for upstairs circulation.

 

[JC22024]

On cold start it will run for 15 or 20 mins then start cycling. Pipes in boiler room are roasting hot and return pipe always only max 25c at any time. (Usually return is stone cold)

I timed the cycling and of course this will vary with temps etc but it will stay off for 2.5 minutes and run again for 1.5mins. Does this constant. Pipes hardly touchable in boiler room so hot. Which makes me think the pump isn't drawing the water quickly enough around the circuit.

As I say I can get all rads to warm up bar one but not cranking enough room heat or near 11c drop.