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Discuss Central heating pump sizing in the Plumbing Forum | Plumbing Advice area at PlumbersForums.net

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172
Hi
I have a valiant plus ecotec 418, ( about 8-9 years old ) it has always had the same problem, continually going from S.5.3 to S5.4 and back again....when ever I check, the Delta T while running normally is around 20oC and I am told S.5.3 doesn’t occur until the DT is 30oC. The boiler fires up very quick, but as the inlet temperature increases only slowly, I assume this is when the 30oC is reached.

it stays in the S.5.3 stage for around 10 minutes, goes to S5.4, then fires up, exceeds the DT then goes back to S.5.3..this cycle continues until eventually it settles down and stays at S.5.4.***..although even before that is achieved, it often fails to reduce firing, even when only 2oC away from the target temperature of 78oC and shuts down on over temperature.

Vaillant tell me it’s likely restricted or undersized pipe work, which could have been due to my ‘ not so very clever’ builder during my house extension in 2003. So if the boiler flow is less than it should be, that could explain why the boiler manages to achieve the outlet temperature so quickly ( I also reduced the KW to between 5-10KW from 18KW ) also if the flow is low, could that explain why the inlet temperature lags behind the outlet temperature so much ???

So would a higher capacity / flow CH pump be the solution ??? The igniter system on this boiler must be excellent, as it fires up so so many times every day, far more than I would consider normal.

thanks
 

scott_d

Plumber
Gas Engineer
Messages
5,451
Can you post some pictures

Is it a big system?
How many radiators?
Unvented hot water cylinder?
What size pipework?
 
Messages
172
10 radiators, vented cylinder, boiler is vailiant plus ecotec 418 (18KW )

not sure how to detail pipe sizes, assume they are standard, NOT microbore.***.

hope images help 🤞
 

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Messages
1,813
Thanks. Boiler primaries appear to be 22mm which is fine for that boiler output and flow required. The pump seems to be discontinued now, so I am struggling to find a data sheet with pump curves etc.
It does initially sound like a flow problem (lack of). Any idea what the quality of system water is like? Are you aware of any sludge buildup or other corrosion? Id imagine with a perfectly healthy system and pump that pump would be fine but again I cant find any info, so might be wrong.
 
Messages
172
Thanks. Boiler primaries appear to be 22mm which is fine for that boiler output and flow required. The pump seems to be discontinued now, so I am struggling to find a data sheet with pump curves etc.
It does initially sound like a flow problem (lack of). Any idea what the quality of system water is like? Are you aware of any sludge buildup or other corrosion? Id imagine with a perfectly healthy system and pump that pump would be fine but again I cant find any info, so might be wrong.
Heating system in good condition, recently drained down, flushed with cleaner and then treated....the water was pretty much clear, save a little discolouration from one or two rads....used to flush every year.***& re treat, then was advised, unless leaks or excessive air, then every 5 years or so is ok

emailed WILO and received the data sheet within 10 minutes, how’s that for customer service 👍
 

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Installing a bigger pump is not the answer. I would be looking for this restriction you mention.
Don’t know how, obviously everything is under floorboards or in walls.******.I would love to tear up all the floorboards and demolish a few cavity walls and re pipe....but that’s out of the question, especially being a 24/7 carer for my disabled Wife, such disruption is not acceptable. I know it’s not ideal, but could a higher output pump resolve the problem ?
 
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