magnaclean filter and low loss header

[doitall]

Lets keep it clean or the mods will lock the thread and no-one wants that.

What you do for a living I have no interest.

As I've said in the past, you are over complicating things, the OP wants a simple cheap fix.

And just why do you think LLH don't blend even if they are crude but affective, so don't come that, I know better.

A shunt pump is installed for the very same reason, to circulate water through the boilers.

But I suspect you know all this anyway.

 

[GaytonTonner]

And just why do you think LLH don't blend even if they are crude but affective, so don't come that, I know better.

You assume the 2 heat Xs cracked because of low flow throw them. They can crack because the delta T is too wide. The blender:

1. Keep the flow up
2. The temperature range within the delta T.

I have explained this. Just like back-end protection. The LLH is approximate and may not aid the flaky heat Xs.

A shunt pump is installed for the very same reason, to circulate water through the boilers.

But do not keep the heat X inside its delta T.

 

[doitall]

But the pump modulation will/should keep the heat x within the delta T, provided you have full circulation.


I don't know much about the Keston boiler or it's faults, but it sounds as though the reverse return may not be a good plan.

 

[ajrobb]

My theories about my broken heat exchangers:
1. it was broken by some warehouseman dropping a pallet.
2. the gate valve restriction in the header circuit allowed a lagging boiler pump to stall

I'm pretty sure I have the boilers working safely with the (now unrestricted) short 28mm primary circuit. Sure, it would be nice if they were efficient too, but I'd much rather they were reliable.

My OP was about trying to improve reliability with a filter. I don't seem to be getting a consensus on that. At the moment I like the look of the 28mm Fernox TF1, as it is both magnetic and cyclonic.

 

[doitall]

As for the filter, I don't think it's a good plan unless you modify the system, as it could be too restrictive.

However it would have to go in the return pipe to the left of the boilers.

As GT the boilermate would be the best if you go ahead.

 

[ajrobb]

I measured several temperatures every minute after a room thermostat cycle for 20 minutes:

Untitled

• ajrobb
• 4 Jan 2011
• 1

The bottom curve is the common return
The middle 2 curves are the boiler returns
The top 3 curves are the boiler and common flows

So at full power, the delta-T across both boilers is 15°C (higher than I thought). The transient delta-T from common return to common flow is about 30°C.

At the current heating load, the delta-T across the boilers is closer to 10°C while the delta-T between flow and return is about 17°C.

 

[doitall]

I can only see three curves.

 

[ajrobb]

I can only see three curves.

The bottom curve is the common return from the radiators.
The middle curves are both boiler returns (they are similar and look like one)
The top curves are the boiler feeds and common feed (they are similar)

 

[doitall]

So you're loosing almost 50% of the flow through the gate valve.

 

[transam]

Used the magnacleans , most of em leaked at one time or another , use the fernox tf now , not had any problems , spiro all brass are probably the best for fit & forget , wether they are better for removing crud well who knows ?

fit one to the return of each boiler !

 

[Onetap]

So you're loosing almost 50% of the flow through the gate valve.

Yes, but then he has two boilers running, presumably with both pumps on maximum. For most of the time he would only need one boiler running, which might cause reverse circulation and reduce the common flow temperature.

The flow in the secondary system is variable. The flow rate through the boilers is controlled by their built-in controllers and can't be affected by the secondary system. The LLH is recommended by the manufacturers, presumably to avoid problems with the heat exchangers due to low flow through the boilers.

 

[doitall]

So you're loosing almost 50% of the flow through the gate valve.

Yes, but then he has two boilers running, presumably with both pumps on maximum. For most of the time he would only need one boiler running, which might cause reverse circulation and reduce the common flow temperature.

The flow in the secondary system is variable. The flow rate through the boilers is controlled by their built-in controllers and can't be affected by the secondary system. The LLH is recommended by the manufacturers, presumably to avoid problems with the heat exchangers due to low flow through the boilers.

Which is what I keep saying he hasn't got a LLH.

He has a reversed return header which is completely different.

I don't know much about Keston or modulating pumps installed in them, but I can see that one or the other running at a lower speed could cause problems.

 

[ajrobb]

So you're loosing almost 50% of the flow through the gate valve.

Yes, at full power, there is twice as much flow through the boilers as through the radiators. So half the boiler flow goes through the gate valve and the other half goes through the radiators (a bit like a low loss header). If I close the gate valve, the delta-T across the boilers would try to rise to 30°C at full power, which is probably why they shut down.

 

[Onetap]

Which is what I keep saying he hasn't got a LLH.

He has a reversed return header which is completely different.

It's a LLH, hydraulic separator, whatever you like to call it.

The reverse return feature is only intended to equalise the boilers' flow rates by making the pipework length the same. The difference, to a direct return, is equivalent to about 700mm of 28mm tube, so it doesn't make any difference.

 

[doitall]

I give up, we're going round in circles.