Inadequate Circulator Pump?

[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.

 

[JC22024]

Good bad or indifferent I just bought a Trident 25/80 180 pump. Cheap enough to test anyway. If I'm wrong then so be it can set on garage shelf! Will be a pain to drain system again to open up pump from 130 to 180 but space to do it.

Really grateful for the great advice on here keep it coming! And of course I will let you all know in any event what difference if any the new pump makes and if it then allows me to balance rads properly without losing circulation.

Just want to keep after it now and get the heating system fully up to snuff if I can.

 

[John.g]

Something very strange going on, assuming boiler flow temp set to 70C then when the burner cuts out with a return temp of 25C means that you are only circulating 6LPM (0.36M3/hr) which equates to the 38W pump output you mentioned previously.
A running time of 37.5% is a average output of 7.5kw with a 20kw boiler or 9.75kw with a 26kw.
Can/have you checked that the circ pump stays running when the burner cuts out.

 

[JC22024]

Something very strange going on, assuming boiler flow temp set to 70C then when the burner cuts out with a return temp of 25C means that you are only circulating 6LPM (0.36M3/hr) which equates to the 38W pump output you mentioned previously.
A running time of 37.5% is a average output of 7.5kw with a 20kw boiler or 9.75kw with a 26kw.
Can/have you checked that the circ pump stays running when the burner cuts out.

Yes pump definitely stats powered up and all heating controls / valves are functioning correctly too

 

[JC22024]

I will check water quality when I drain it again and if dirty at all then I'll get more cleaner and run again with new larger pump. But water now coming out of rad vents is practically clear.

I do flush it out every few years too. I recall first time I did it when I was about 18 the water was pitch black and some rads had to come off and be flushed out with hose. Again this was 15 - 20 years ago.

 

[JC22024]

Upstairs has been running on its own tonight for a couple hours. 2 double rads hot and bathroom tall single hot.

On time = 1.5 mins. Off time= 4 mins 45 secs.

Return temp 43c




Again on the small upstairs zone I can get all rads warm. But when I balance first 2 correctly the rest fall off cold even with valves fully open.

It's on the larger downstairs circuit that the return temp never rises above 25c even after hours of running.

 

[John.g]

Be interesting to see how this pump performs, you may as well clean that mag. filter as well after any flushing etc.

 

[ShaunCorbs]

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

Yes 25mm bore 8m head

 

[ShaunCorbs]

Could you freeze one side and adjust the pipe/ pump valve sages draining down ?

 

[JC22024]

Could you freeze one side and adjust the pipe/ pump valve sages draining down ?

Yes probably could freeze it except I don't have any of that equipment!

It's easy enough to drain down anyway I suppose. stopcock for header tank easily reachable at trap door. Pop hose on boiler and let it run. If I don't crack the bleed screws on the rads most of them tend to stay full anyway.

New pump dispatched today by 24hr service so should have it tomorrow and will tackle replacement Friday night probably need to pick up some 28mm olives too.

 

[John.g]

Upstairs has been running on its own tonight for a couple hours. 2 double rads hot and bathroom tall single hot.

On time = 1.5 mins. Off time= 4 mins 45 secs.

Return temp 43c

View attachment 67200
View attachment 67201

Again on the small upstairs zone I can get all rads warm. But when I balance first 2 correctly the rest fall off cold even with valves fully open.

It's on the larger downstairs circuit that the return temp never rises above 25c even after hours of running.

Is the boiler firing or not with that temp of 89.5C?.

 

[JC22024]

Is the boiler firing or not with that temp of 89.5C?

Those temps were taken whilst the heating was running can't remember exactly if the boiler was firing at that exact moment but the temp would be fairly consistent in any case.

 

[John.g]

I think the max boiler setpoint temp on that boiler is 75C or maybe just 80C max?. Can you ensure that the pump is pumping away from the boiler and what is the power showing there, it looks like 13W? What is the boiler stat set to? there is a 28mm? copper elbow under the boiler stat, is that the vent?.

 

[JC22024]

I think the max boiler setpoint temp on that boiler is 75C or maybe just 80C max?. Can you ensure that the pump is pumping away from the boiler and what is the power showing there, it looks like 13W? What is the boiler stat set to? there is a 28mm? copper elbow under the boiler stat, is that the vent?.

Yes pump is on outlet and arrow pointing away from boiler.

Not sure why the reading appeared so high yesterday. After upstairs running a few hours checked now and boiler outlet high 70s. yes open vent at top rear right.

Ps just thinking I did actually turn boiler stat down since last night!

 

[John.g]

Thanks, that very high temp of 89C might cause the pump to cavitate and cause circulation problems, might try a SP of ~ 70C for tomorrow and see what the pump power is. Can you see what that power reading was above, looks like 13W to me.

 

[JC22024]

Thanks, that very high temp of 89C might cause the pump to cavitate and cause circulation problems, might try a SP of ~ 70C for tomorrow and see what the pump power is. Can you see what that power reading was above, looks like 13W to me.

Thanks yes I was wondering the same thing last night and turned the temp down a little. Will turn down some more too to hit 70 as you suggest.

The wilo pump is still in there and I'll likely just put the Trident pump in next so can't see the pump power readings any more at the moment.

 

[John.g]

OK thanks again, can see tomorrow what the 70C does, if anything, you will soon know as the boiler dT will decrease if the pump is circulating more.

 

[JC22024]

OK thanks again, can see tomorrow what the 70C does, if anything, you will soon know as the boiler dT will decrease if the pump is circulating more.

Thanks I did turn it down more this morning and ran for 1.5 hrs before I left for work on downstairs zone. Didn't appear to make a difference on the rads not heating decently. Indeed they felt cooler. But will be sure to test this with new pump also incase the boiler is actually boiling the water at high settings! Which it could well be too adding to problems.

 

[John.g]

Presume boiler only ran continuously for 20 minutes or so and then started cycling??.

 

[JC22024]

Presume boiler only ran continuously for 20 minutes or so and then started cycling??.

Correct yes. I did get the olives etc this morning and DHL delivered new pump. So I'll fit it tonight when home from work, refill and properly time the boiler start up run time on GF zone. And see if the rads perform better. Fingers crossed!

 

[JC22024]

System draining down, this is the water coming out (I believe the system shouldn't have blockages. Water is always clean coming out)