magnaclean filter and low loss header

[GaytonTonner]

As Doitall wrote, you do not have a low-loss header, it is a reverse return. Well it looks that way from the picture.

Your prime problem is preventing heat exchanger cracks. First find out what the delta T (temperature differential between F & R) is. If it is say, 20C, then determine the flow temperature and fit a blending valve on the common return to the boilers. Set this at 20C below the setpoint of the boilers. If the boilers setpoint is say 75C, then set the blending valve to 55C. This ensures that the return temperature does not fall, below 55C. Too wide a Deta T can crack the heat exchangers, as you know. Then the boilers are operating with their comfort range.

The blending valve is giving back-end protection. This was to stop non-condensing boilers condensing and rotting the insides of boiler burner boxes. In your case it is to stop heat X cracks.

If you set the boiler to say 75C, 75C will enter the cylinder coil giving a quick warm up, yet the return temperature will not be say 30C. The boilers cycle on themselves partially. They fully cycle on themselves on cold start until above 55C return. The valve slowly opens sending water to the cylinder/CH circuit keeping the boilers Delta T in check.

 

[doitall]

You don't have an LLH. other than the by-pass will act as one.

If one pump is running slower it can stall but circulation will still take place because of the reverse return.

 

[ajrobb]

A simple straight forward reverse return set up

I don't understand. The two boiler pumps put most of their flow through the gate valve. The (third) primary pump diverts some of the flow to the radiators and/or HWC. The gate valve is at boiler flow temperature. How is the return reversed?

 

[doitall]

A simple straight forward reverse return set up

I don't understand. The two boiler pumps put most of their flow through the gate valve. The (third) primary pump diverts some of the flow to the radiators and/or HWC. The gate valve is at boiler flow temperature. How is the return reversed?

The gate valve should be an auto by-pass valve (AVDO) are best.

If you look at the pipework to the boiler, the flow is the first tee from the first boiler, and the return is the first tee from the 2nd boiler.

So the flow goes 1-2 and the return goes 2-1.

 

[doitall]

This is exactly the same set up with multiple zones

Untitled

• doitall
• 2 Jan 2011
• 5

 

[ajrobb]

Untitled

• ajrobb
• 2 Jan 2011
• 1

I may have been confusing the issue by calling the radiator circuit the primary circuit.

 

[ajrobb]

This is exactly the same set up with multiple zones

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• doitall
• 2 Jan 2011
• 5

I don't see a secondary circulation pump there and it has a by-pass, which mine doesn't

 

[doitall]

The pump on the left in your pic is the main primary circulation pump, it sends the water to where ever it splits for the cylinder and heating valves. S plan or Y plan.

For the record the pump is doing exactly the same job as the pumps in the boiler, and shouldn't be needed

 

[ajrobb]

shouldn't be needed

Given that the gate valve is currently wide open to maximise flow through the boilers to protect the all-too-delicate heat exchangers, there would be no circulation through the radiators without the third secondary pump.

 

[doitall]

But as I said that valve shouldn't be there, it should be an auto by pass valve as in my pic.

And it isn't a secondary pump, its just boosting the other two, (doing the same job)

This is a low loss header, signed and installed by doitall (thescruff)

View media item 29587

 

[GaytonTonner]

shouldn't be needed

Given that the gate valve is currently wide open to maximise flow through the boilers to protect the all-too-delicate heat exchangers, there would be no circulation through the radiators without the third secondary pump.

I would remove the third pump. Have blending valve with the outlet of the valve attached to the black pipe in your dia. Do away with the red pipe with the gate valve in. The red flow from the boilers go into the hot port. The blue pipe (return) goes to the cold port. Set the valve as I suggested.

 

[ajrobb]

This is a low loss header, signed and installed by doitall (thescruff)

I see no difference topologically between that and my system. OK, there is a large vertical pipe instead of a shorter horizontal pipe and expansion vessel. Two parallel external primary pumps and two boilers instead of two parallel internal primary pumps in two boilers. One problem I have is that my primary pumps are modulated by the boilers so might stall if not at the same speed.

I would remove the third pump.

Even with the third (secondary circulation) pump on max and TRVs open, starting from cold the boilers cut out with insufficient flow if I close the gate valve. I can't imagine that removing the pump would increase circulation. If I fitted an ABV in an attempt to give the boilers sufficient flow, I doubt I get sufficient flow through the radiators.

 

[Boilerman2]

It is the Diameter of the Pipe that makes it a "Low Loss Header" the clue is in the name! what you have is a simple Shunt circuit between the flow & return the loop is undersized and so acnnot be refered to as a LLH !

Nice Remeha Quinta's by the way!

 

[Norcon]

This system has already been discussed on this thread....

//www.diynot.com/forums/viewtopic.php?t=239878&postdays=0&postorder=asc&start=0

 

[doitall]

To get it out of the way the two are completely different, with the header the two boiler pumps act as shunt pumps to circulate the water around the header, then the system pumps draw water from the header.

Ok back on track.

With a reverse return system both pump work independently of each other, you can actually turn one of the boilers off and it will make no different to how it works, in fact it's common to have a lead and lag boiler so one fires up first and the other cuts in when needed, the same as hot water you only need one running.

The only thing I would alter if you're getting low flow rates is increase the header pipes to 42-54mm.

I would remove the gate valve and fit an AVDO auto by-pass valve.

What happens to the primary pipes, do they go into a 3port valve or two 2 port valves, a pic of that area would help.

Another alternative is to bring all the MV's back to the boiler and run the zones from there, 1st pic, it would give you a much better flow to the cylinders and rads.

The only other choice is a proper header as in the last pic.

What is the size of the property. how many radiators etc.