Circulation Pump Question

[NorthernLad]

As mentioned in my 'System Drain' thread the house has been extended in 1986. In recent years I felt the circulation was not as good as it should be
.
I have previously replaced a section of pipe when we had blockage at point where cold feed joins together with clean and drain, refill+ inhibitor
About 4 years ago I also replaced the pump like for like Grundfos UPS2 15-50/60.

(As an aside I think I read the set up for open system should idealy be V P C whereas ours is C V P which may partially account for the blockage?)

Having read threads on here I now wonder if in fact the pump been never been big enough to service the pipework we have.

Following the extension its now a long thin house with the extension end being fed by pipework from upstairs to an extra bedroom and 2 drops to ground floor.
That end of the house and in fact the room at the opposite end dont seem to be receiving the full flow. The boiler is downstairs to the right end and the pump is upstairs to left of centre.
I have balanced and most rads in the centre upstairs are only 1/16 open to ensure downstairs gets sufficient flow. I also throttled the feed to the DHW cylinder.
(Without any balancing the upstairs gets all the flow and downstairs gets zero)

End to end the radiator locations are 15 metres apart.
Upstairs there are 11 rads ranging from towel rails to 6 foot single panels (I drained 95 litres from these)
Downstairs there are 7 rads ranging from 2 foot singles to 6 foot doubles. (Not been able to drain yet but guessing similar volume)

Should I consider a larger pump? Or may I then have a pump-over issue?

 

[SJB060685]

Sounds to me the pump head isn’t enough to overcome the index circuit. What boiler do you have and is the pump mounted externally to the boiler?

 

[king of pipes]

A Dab evosta 3 will do what you need a very versatile adjustable pump . Kop

 

[John.g]

18 rads so pointing to a 8M pump but the dab Evodta 2 which is a 7M pump will probably do the job. The Evosta3 is a 6M pump and gives lovely information of pump head, pump flow and Pump power but the Evosta 2 is a better choice IMO.

You can also get a 8M Evosta2 or a 8M Evosta3. (see Dab Evosta 2.pdf)

 

[ShaunCorbs]

Do they receive flow if you shut 5 rads off ?

 

[king of pipes]

Dab evosta 3 I recommend is a 8 m head pump. Kop

 

[NorthernLad]

SJB060685 -
Boiler is a Potterton Netaheat 16-22 - do I win the prize for the oldest still working?
Boiler is downstairs Pump is upstairs Horizontal separation is about 8 metres.

KOP -
Could I end up with a pump over problem if pump too strong?
I thought I had that problem but its just expansion up through feed pipe because I can see pattern of a small amount of debris on the floor of the two F&E tanks

John.g -
Thanks for that. I will have to study hard to understand the info for the various Evosta pumps! I am a bit blinded by the graphs to be honest. Am I reading correctly that the inlet/outlet are in inches?

Shaun - Well, I can balance to get flow to all at the same time but not enough overall heat in winter.
For much of the year we dont need 5 of the rads - the upstairs part of the extension is 3 of those rads, so its only in winter we are just keeping those on minimum. I suppose the short answer to your question is Yes.

EVOSTA2 40-70/*** M230/50-60 6.9 Hmax [m] 3.6 Qmax [m3/h]
EVOSTA3 80/*** M230/50-60 8 '' 4.2 ''
So if you are suggesting pumps for 7 or 8 metres, as above, am I right in thinking that the present Grundfos isn't really up to the job its being asked to do?
I never looked before but now see 15 means inlet/outlet in mm - (its fitted on 22mm pipework) and the 50/60 means 5/6 meters.

One final point about the ancient boiler it does cycle on/off every three minutes which I am aware isnt exactly right!
I am guessing that a higher rated pump would give faster flow rate and this cycling would not occur - or is that a misunderstanding I have?

Would just like to add my appreciation to all of you on here. It seems to me that you are on here almost every day come rain or shine giving freely of your time and widespread knowledge to the uninitiated.
The world needs more people like you.

 

[ShaunCorbs]

Sorry I mean if you turn 5 off via trvs does the rest eg the other ones that didn’t / slow to heat up ?

 

[SJB060685]

If you balance and get flow to all radiators that suggests the pump is circulating fine. What output is the boiler? What is the new load after the extension?

 

[NorthernLad]

Ah, just discovered quote facility!

Sorry I mean if you turn 5 off via trvs does the rest eg the other ones that didn’t / slow to heat up ?

Yes -The rest would eventually heat up.

If you balance and get flow to all radiators that suggests the pump is circulating fine. What output is the boiler? What is the new load after the extension?

Boiler is, I assume, 16-22Kw as per post #7 few minutes ago.
They added 3 extra rads upstairs and two downstairs.

 

[SJB060685]

Ah, just discovered quote facility!

Yes -The rest would eventually heat up.


Boiler is, I assume, 16-22Kw as per post #7 few minutes ago.
They added 3 extra rads upstairs and two downstairs.

Ah sorry mate I didn’t notice that. Based on what you’ve recently said I’m leaning towards a possible undersized boiler.

 

[ShaunCorbs]

Would say pump depending on what the boiler is doing eg keeping up with demand etc

 

[king of pipes]

Providing the system is piped correctly then it shouldn't be a issue there are thing that can be done to overcome the problem should it occur, I would give the system a good clean out before doing anything put some cleaning chemicals in the system for a week and let it work as normal , I am in the process of doing one myself I like to drain the header tank disconnect it connect up the mains cold to the tank outlet with some speed fit blank off the vent lock open the zone valves , connect up a hose either to a low level drain point or remove a rad and use the valves as flushing points then flush all the dirt and debris from above this can easily take all day so allow plenty of time , once completed refill and a quality inhibitor . Kop

 

[king of pipes]

Ah sorry mate I didn’t notice that. Based on what you’ve recently said I’m leaning towards a possible undersized boiler.

If it was undersized then it wouldn't turn off on temperature ? it needs gas rating and setting to its max output a good clean out is needed first is my advice . Kop

 

[SJB060685]

If it was undersized then it wouldn't turn off on temperature ? it needs gas rating and setting to its max output a good clean out is needed first is my advice . Kop

You make a good point, I had forgotten he mentioned it cycling.
Yes if undersized then it wouldn’t do that. The energy leaving the boiler would be lost across the system emitters and the flow temperature shouldn’t ever rise to the point the burner cycles.

 

[John.g]

Cycling on/off every 3 minutes? so if a non modulating boiler, output is only either 8kw or 11kw so something amiss with 18 rads.
If one assumes 25kw total rad demand, then the circ rate required is 30LPM (1.8M3/hr) at a dT of 12C.
Check that the present pump is set to max speed, setting 3 or III.

 

[NorthernLad]

John g - yes pump is currently on setting 3 so getting the best I can out of it.

Firstly I am going to add a 'valve with drain cock' to older part of system and finish the cleaning part of the job. (KOP -Having done the upstairs rads yesterday I can confirm it is time consuming!)
To change that valve and with two F&E tanks I will need four rubber plugs to form a vaccum - Toolstation sell, but theirs have a step instead of smooth cone shape and I read that was better (?) - can anyone suggest alternative?

Once clean I will get the pump changed and see what result I get. This part will take place in the warmer weather and I will let you know because I know you like to have an ending to the story!

Really grateful for all your input.

 

[SJB060685]

Any chance you have a means of measuring the delta T across the boiler? As in what the return temperature into the boiler is and the flow out temperature.

 

[John.g]

Two F&E Tanks, why do you have two?.

 

[NorthernLad]

Any chance you have a means of measuring the delta T across the boiler? As in what the return temperature into the boiler is and the flow out temperature.

I dont, but guess I could get a device to measure that. Any recomendations? What might that show or prove one way or the other?

Two F&E Tanks, why do you have two?.

Good question - Answer is I dont know because I didnt live here when they were installed.
My best guess is this was done at the time of the extension and again only a guess that one ends up at some other point in the system.
The lady of the house at the time was a bit keen on having everything covered up so I cant see where the pipes end up.

The loft had been given fibreboard walls 'to provide a playroom for the kids' and I had to cut the wooden frame and remove a section of this just to get at the F&E tanks. This is just one example.
The buider who did this must have seen the £ signs but the trade guys he used couldnt build a straight line - they actually plastered over wallpaper at one join...

 

[SJB060685]

I have a laser pointer that measures temperatures. You can get clamp on stats that measure the DT but that’s money you don’t really need to spend.
A simple digital thermometer would work and pretty cheap from places like tool station etc.
Being an old non condensing boiler you should be looking at a ΔT across the boiler of about 11-12°c. If it’s more than that that would indicate poor circulation and possibly why you’re experiencing the burner cycling. Poor flow could be due to a fouled heat exchanger or a problem in the system somewhere.

 

[NorthernLad]

Many thanks for that - I will take a look ready for when my cleaning is completed so I end up with the best possible readings.