Bigger Pump ?

[ChrisR]

One point which has not been considered is whether the boiler has been range rated.

Yes it has. The post you just read.

A 22mm pipe has a resistance of ~0.1 metres per metre length.

SO it's a fixed figure?
Drivel !
It depends on the flow rate
Which you got wrong before, now you have the resistance wrong.

The 15/50 can handle a head of ~2m at 0.63 l/s

No, that's wrong too. It's about 3m, but you have to allow for the boiler, valves etc.

metres of 22mm pipe. That does not take into account the 15mm pipework and the resistance of the radiators etc.

Well whoopy do, that's a bit obvious though, and having shown the pump is too small there's little point considering extra resistance.

Not having a good time are you.

Hailsham, someone (else) might look forward to you writing something which is not either

wrong, or
irrelevant, or
bleeding obvious.

 

[D_Hailsham]

I know what the instructions on X400 say.
It doesn't apply to all Powerflushing.

The OP does not say anything about having the system power flushed. His description implies that it was not pwerflushed.

And if he has a rad right next to the pump your "method" won't work, so there's two reasons why it's wrong.

Are you thinking of a rad, e.g towel rail, used as a bypass; i.e before the motorized valves?
What is the second reason?

No it wasn't just a typo. If you'd realised the consequences of what you wrote you'd have seen it was obviously wrong.

I'm not going to argue this point - no one can win.

Change the pump yours is too small. I already told you that and I've given you reasons and figures.

Probably correct about the size of pump.even if your figures are incorrect.

However, if, as is quite likely:
Your rads don't need a 100kBtu boiler.
Your pipework is undersized
You may not be correct about the boiler being on (firing) all the time
The boiler may be range rated (ie downwards)

Agreed, which is why I suggested Sedbuk Boiler Sizer and the Stelrad Catalogue.

 

[D_Hailsham]

A 22mm pipe has a resistance of ~0.1 metres per metre length.

So it's a fixed figure? It depends on the flow rate.

I know it depends on the flow rate. To spell it out for you, at 0.63 l/s (38 l/m) the resistance of a 22mm pipe is approximately 0.1 metres per metre length. And you still have not explained where you get the figure of 2 metres head in 6 metres of pipe.

The 15/50 can handle a head of ~2m at 0.63 l/s

No, that's wrong too. It's about 3m

Had another look at the Grundfos Selectric Graphs. At 0.63l/s, the 15/50 will handle ~2m and the 15/60 ~ 2.7m.

bleeding obvious.

It may not be obvious to the OP

 

[Agile]

The correct starting point is to measure the power output of the boiler and compare that with the heat output of the rads to ensure that they are matched.

One point which has not been considered is whether the boiler has been range rated. .

I dont know why you have said that!

The whole reason that I said that the starting point is to measure the boiler output power is precisely to find out what it actually is !

Tony

 

[ChrisR]

Jeeeeesus

ChrisR wrote:

I know what the instructions on X400 say.
It doesn't apply to all Powerflushing.

The OP does not say anything about having the system power flushed. His description implies that it was not pwerflushed.

No, he didn't. But YOU DID:

So it wasn't a power flush then? If so, the flushing solution needs to circulate for at least two days and preferably as much as 4 weeks.

NOW do you see? Don't bother answering.

Quote:
Quote:
The 15/50 can handle a head of ~2m at 0.63 l/s

No, that's wrong too. It's about 3m

Had another look at the Grundfos Selectric Graphs. At 0.63l/s, the 15/50 will handle ~2m and the 15/60 ~ 2.7m.

I do hope you will accept that the red line shows half way between 0.5 and 0.75 which is 0.625 which is close enough to 0.63

I could do the same from 3 sources for the pipe resistance but you aren't worth the trouble.

 

[D_Hailsham]

No, he didn't. But YOU DID:

So it wasn't a power flush then? If so, the flushing solution needs to circulate for at least two days and preferably as much as 4 weeks.

NOW do you see? Don't bother answering.

Why shouldn't I reply when you have based all your argument on a misinterpretation of what I wrote? If so, means: if my assumption, that it was not a power flush is correct; i.e if it was not a power flush. You are taking it to mean: "if it was a power flush".

I do hope you will accept that the red line shows half way between 0.5 and 0.75 which is 0.625 which is close enough to 0.63

Grundfos seem to have changed their specifications as my figures are taken from their current info, which can be downloaded from Here

I could do the same from 3 sources for the pipe resistance

OK then. You originally said: More like 0.63 l/s . At that rate a 15/50 will give you at max a couple of metres head for the pipework. Which in 22mm is enough for about 6 metres length. 3 metres flow + 3 metres return. Probably not enough for your house??
What is your source which says that 6m of 22mm pipe has a resistance of 2m?

 

[namsag]

Not reading too deep into this little discussion, but one thing that you will learn with CH is at times systems will appear to disregard all laws of physics and not work when it should and everything is right and on other occasions work perfect when there is no way it should this job never fails to throw up surprises.

To the OP the first thing i would be checking is the actual working pressures of the boiler and the gas rate to make sure it was getting eough heat into it for whatever size pump to circulate it around the system.
As your boiler is continually firing without cutting off it sounds very much like this is the actual problem , it would not be the first time someone has adjusted the appliance govenor right down to stop a boiler being noisy or for some other reason.

 

[billm]

Sorted.

I followed the advice given on here and balanced all the rads in the correct order and manner. The boiler was cycling after an hour but I couldn't work out why some of the upstairs rads were still only lukewarm. So I followed the pipes from the boiler.....

It transpired that the first device the pipes came across was upstairs on the landing - the hot water cylinder - and the valve on that was wide open nicking all the heat. Once I shut that off the remaining rads became hot and I was able to balance them as instructed on here. Finally I cracked open the hot water cylinder valve a fraction just enough to get a reasonable temperature drop across the inlet and outlet pipes to warm the water cyl.

Before all that I drained and stuck 2L X400 cleaner in the system and will leave that to circulate for a few weeks before draining, flushing and then refilling with X100.

So it looks like the cylinder was acting like an unrestricted bypass and was the problem afterall. Many thanks to everyone who gave advice - I couldn't have done it without your help.

cheers Bill

 

[Agile]

Sorted.

It transpired that the first device the pipes came across was upstairs on the landing - the hot water cylinder - and the valve on that was wide open nicking all the heat. Once I shut that off the remaining rads became hot and I was able to balance them as instructed on here.

So it looks like the cylinder was acting like an unrestricted bypass and was the problem afterall. Many thanks to everyone who gave advice - I couldn't have done it without your help.

cheers Bill

You have now learnt something that 95% of installers dont even realise, the need to balance the cylinder with the system!

A few installers will explain their desire to save £5 by omitting a gate valve by saying that the cylinder will be given priority.

Of course thats nonsense as a balancing valve is required to enable the system to be adjusted to give the desired heat input to the cylinder.

In any case with a condensing boiler its important to set the flow rate through the cylinder to enable the boiler to operate more efficiently.

Tony

 

[Norcon]

I agree about the balancing valve adjusting the correct flowrate through the cylinder to acheive the correct heat exchange rate but restricting the flow through the cylinder heat exchanger to balance the flow with the CH circuit is just plain stupid.

 

[Agile]

but restricting the flow through the cylinder heat exchanger to balance the flow with the CH circuit is just plain stupid.

Would you like to explain that assertion in technical terms?


Tony

 

[Norcon]

I didn't think it needed explaining .
You are treating the cylinder heat exchanger as another radiator in the system and as such the flowrate will be much too low.

 

[gas4you]

Unless you have a fast recovery cylinder fitted. In that case you do not want a balancing valve on the cylinder circuit, as if you do have one, it will stop the HW cylinder being a fast recovery one