Central heating pump sizing

[Reddwarf4ever]

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]

Can you post some pictures

Is it a big system?
How many radiators?
Unvented hot water cylinder?
What size pipework?

 

[SJB060685]

As above a bit more info would help.
Boiler output.
System load.
Boiler pipe sizes.
Current pump specs.

 

[Reddwarf4ever]

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 🤞

 

[SJB060685]

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.

 

[Reddwarf4ever]

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 👍

 

[ShaunCorbs]

15-60 will be fine

but suspect the issue is your microbore pipe work

 

[SJB060685]

That is good customer service. The pump if healthy is suitable by the looks of it.

 

[Reddwarf4ever]

15-60 will be fine

but suspect the issue is your microbore pipe work

DONT have microbore pipe work 🤯

 

[Reddwarf4ever]

That is good customer service. The pump if healthy is suitable by the looks of it.

As it looks as though, some restriction was created during the CH re site during the extension build.....could a pump,with a higher output help resolve the issue ??? Thanks

 

[SJB060685]

Installing a bigger pump is not the answer. I would be looking for this restriction you mention.

 

[Reddwarf4ever]

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 ?

 

[SJB060685]

A higher output pump is going to cause more issues at the boiler. @ShaunCorbs what about CCT'S at the boiler?

 

[Reddwarf4ever]

A higher output pump is going to cause more issues at the boiler. @ShaunCorbs what about CCT'S at the boiler?

What are CCTs ?

saw this chart for adjusting burner anti cycle time, can’t understand how the chart works....though that it was a simple matter of entering a value in minutes 🤯

 

[ShaunCorbs]

DONT have microbore pipe work 🤯

sorry misread

 

[ShaunCorbs]

A higher output pump is going to cause more issues at the boiler. @ShaunCorbs what about CCT'S at the boiler?

I wouldn’t say you need a bigger pump it’s only going to cause more problems

 

[ShaunCorbs]

What are CCTs ?

saw this chart for adjusting burner anti cycle time, can’t understand how the chart works....though that it was a simple matter of entering a value in minutes 🤯

close coupled tees allows you to fit a bigger pump

 

[SJB060685]

CCT's (close coupled tee's) as Shaun says will separate the system hydronically. This will allow another pump to be installed and different flow rates in each part of the system while maintaining the right flow through the boiler.
Can I assume if you're experiencing flow problems then some if not all radiators are struggling to heat while the boiler is running?

 

[Reddwarf4ever]

CCT's (close coupled tee's) as Shaun says will separate the system hydronically. This will allow another pump to be installed and different flow rates in each part of the system while maintaining the right flow through the boiler.
Can I assume if you're experiencing flow problems then some if not all radiators are struggling to heat while the boiler is running?

None of the radiators struggle to get hot.....they all struggle when the boiler is cycling 5.3 to 5.4.....once it settles down, everything is really hot.......found a pump on eBay where the wattage is 93W on high compared to 65W on my present one, does that imply it’s more powerful or just uses more power to do the same thing ? don’t want to modify the system.......I assume the 30oC Delta T setting can’t be changed, also not sure why it’s there, efficiency or boiler protection thanks

 

[SJB060685]

That wattage will be its power consumption, which obviously increases with a more powerful pump and the higher the setting. With 22mm primaries and a larger pump I imagine more problems with boiler delta t.

 

[ShaunCorbs]

Have you tried balancing the system should be around a 10 dc drop on the rad flow and returns ?

 

[John.g]

None of the radiators struggle to get hot..they all struggle when the boiler is cycling 5.3 to 5.4..once it settles down, everything is really hot....found a pump on eBay where the wattage is 93W on high compared to 65W on my present one, does that imply it’s more powerful or just uses more power to do the same thing ? don’t want to modify the system....I assume the 30oC Delta T setting can’t be changed, also not sure why it’s there, efficiency or boiler protection thanks

You might consider a A rated pump which displays the power in watts from which you can easily deduce the flow rate and pump head and at least you can rule this in or out then, as suggested above a 6M pump should be quite adequate, I have 10 rads and a 20 kw OF boiler and the pump (6M wilo yonos Pico) power gives a flow rate of 12 LPM @ 3.2M head which is quite accurate as the boiler deltaT is ~ 25C., this pump only cost me ~ £100 two years ago.

 

[Reddwarf4ever]

That wattage will be its power consumption, which obviously increases with a more powerful pump and the higher the setting. With 22mm primaries and a larger pump I imagine more problems with boiler delta t.

Hi
to my way of thinking, a more powerful pump = higher flow rate, the heat dissipation from the rads would not increase as It’s down to Delta T Rad Vs Room temperature, therefore the return temperature would be higher, the boiler has no issue heating, so does this make sense ? Higher flow rate = increased inlet temperature therefore boiler Delta T would fall.....

Also is wattage such an accurate way to determine flow ? As these pumps are centrifugal, power would not exactly relate to flow, as with a reciprocating positive displacement pump ?

 

[Reddwarf4ever]

Have you tried balancing the system should be around a 10 dc drop on the rad flow and returns ?

Hello have TRVs fitted to all rads except the top landing Hall and lounge ( 4 rads ) needs these fully on, works well....don’t think balancing is appropriate.....the rad flow return Delta T, is that the same as across the boiler, effectively, when on heating only ?

 

[ShaunCorbs]

Hello have TRVs fitted to all rads except the top landing Hall and lounge ( 4 rads ) needs these fully on, works well....don’t think balancing is appropriate.***.the rad flow return Delta T, is that the same as across the boiler, effectively, when on heating only ?

you should be getting around 15dc split / delta across the flow and return at the boiler

eg

flow 65
Return 50