Inadequate Circulator Pump?

[JC22024]

What pump setting? and what are boiler flow/return temps as flow rate can be calculated from this.

Setting 3, I'll let it run a little longer then record temps. Boiler should be putting out 26kw approx as that is the nozzle and settings I have it at.

 

[John.g]

While its running, pop up to the attic and look for any movement in the F&E tank, hold a "glass" of water with the vent immersed in it and see if any water is being drawn in, also, later, get someone to stop/start the boiler/pump and watch for any pump over or tank surging when the pump starts or stops. IMO 6M on that capacity pump would be more than adequate and 5M would probably fit the bill as well as its so big that it will run like a constant pressure pump on any one of those settings.

What is the Boiler SP.

 

[JC22024]

While its running, pop up to the attic and look for any movement in the F&E tank, hold a "glass" of water with the vent immersed in it and see if any water is being drawn in, also, later, get someone to stop/start the boiler/pump and watch for any pump over or tank surging when the pump starts or stops. IMO 6M on that capacity pump would be more than adequate and 5M would probably fit the bill as well as its so big that it will run like a constant pressure pump on any one of those settings.

What is the Boiler SP.

There are 3no vents up there. Tested all 3x and no water being drawn in. 1 of them slightly bobbed the water up and down a little but did not suck it in just slight movement of water. And one tiny bubble came out of it. I presume that's the one that comes from the boiler. The other 2 I know 1 comes from a large hunter stove and the other not sure maybe redundant from back boiler fire / range cooker that both were done away with years ago.

 

[JC22024]

What does boiler SP refer to?

Here are temps now

ALL downstairs rads toasty now.

 

[JC22024]

I have a theory here of what was happening.

The pump was always undersized. However with the old boiler it was just about functional and balancing still wasn't right but "good enough"

New condensing boiler definitely made it lie down dead pressure wise. I believe the new boiler is harder to pump water through the jacket. Maybe due to heat exchanger etc.

Additionally, when the water flow was well down the new boiler was getting up to temp too fast and too high. Also cavitating the pump for good measure. There were times I could hear the boiler boiling the water.

 

[John.g]

Boiler SP is the boiler thermostat setpoint, I would dial that down another 2 divisions to give ~ SP of 75C.
Your flow/return temps above of 81.1/47.8 = dT of 33.3C and with a boiler output of 26kw = flowrate of 11.2 LPM so still a big resistance somewhere IMO as ~ 3/3.5M head should easily give you that flow rate.
The resistance of that boiler Hx is negligible like all oil fired boilers, where the Hx is basically a box full of water, its only 0.19mbar, a fraction of a meter.

If the Alpha (or any 6M) pump was operating correctly the you would have still got 9.6LPM, the new pump will give the same 9.6LPM at 6M (speed2)

 

[John.g]

Is the hunter stove in use at times for CH,?

 

[ShaunCorbs]

I have a theory here of what was happening.

The pump was always undersized. However with the old boiler it was just about functional and balancing still wasn't right but "good enough"

New condensing boiler definitely made it lie down dead pressure wise. I believe the new boiler is harder to pump water through the jacket. Maybe due to heat exchanger etc.

Additionally, when the water flow was well down the new boiler was getting up to temp too fast and too high. Also cavitating the pump for good measure. There were times I could hear the boiler boiling the water.

Probably working on gravity circulation as well / helping hand now around 60 won’t work as much so more strain on an undersized pump so I guess your happy now ?

 

[JC22024]

Is the hunter stove in use at times for CH,?

Literally never. Lit at Christmas once every 2 years. Should use it more!! Or move it into a room where it will actually get used. (Im dining room) it is a big one - 32kw or something total.

Probably working on gravity circulation as well / helping hand now around 60 won’t work as much so more strain on an undersized pump so I guess your happy now ?

Yes amazed at the difference and the house definitely needed this size of pump. Thanks for the recommendations there of 25 / 80!

All rads were hot tonight. I could probably jet boiler back down to 20kw but will run it into Jan this way anyway before deciding. House never had such good heating as right now. Lived here all my life so I know the heating system very well and how the house feels. This is amazing now.

I did also turn boiler stat down a couple notches as suggested by John as rads were almost scalding.

Not sure how John's calcs are determined above, wouldn't ambient temperatures and actual room temperatures severely influence any such calculation? I think its all running very good now.

Header tank doesn't appear to be doing anything stupid but left trap door off and will monitor. Also need to replenish inhibitor now I drained it out.

Will clean mag filter every week now for foreseeable until I see it totally clean. I do get very slight buildup after it was installed so I suppose its doing a great job at capturing anything in this old system.

 

[John.g]

Will explain general calcs tomorrow which you might find interesting.

Re d/stairs, are some of the lock shield valves throttled in and have all got TRVs fitted?