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PostPosted: Wed Nov 16, 2016 10:28 am 
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I was just wondering if I had missed any flaws in my cunning plan.

I have 10 radiators all fed by 8mm microbore from manifolds. The system ( generally ) works fine, pump is set to the second speed ( of three ).

However, one radiator takes quite a bit longer to heat up than the others. Once up to temperature, it's fine. Although this radiator is old ( 30+ years ) it is still working and in good condition ( no cold spots ).

The problem I believe is that this radiator is the furthest from the boiler and being the largest radiator in the house AND double panel it just isn't getting the flow it needs to warm up as quickly as the other radiators.

The issue wasn't really apparent when we bought the house, but it has been noted that the radiator has taken longer to warm up each time the house has been extended ( twice ) and radiators added.

So my cunning plan is this. The manifold is a dual 8mm/10mm type. The ports are sleeved with easily removable reducers to allow the use of 8mm pipe. So, if I were to run 10mm pipe between this one radiator and the manifold ( easy job ) I will then improve the flow through this one big radiator.

I anticipate that there will probably be a small effect on the other radiators but other than that I can't see a problem with the plan.

I'm not an expert in fluid dynamics so have I missed anything?

Thanks.


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PostPosted: Wed Nov 16, 2016 10:44 am 
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And what size is the manifold pipe and how many radiators are fen from it.

Why is the pump on 2 and not 3


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PostPosted: Wed Nov 16, 2016 11:44 am 
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Sounds like a balancing problem to me, you probably need to restrict flow to some of the radiators closest to the boiler in order to allow more flow to the furthest radiator.


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PostPosted: Wed Nov 16, 2016 11:58 am 
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Rorschach wrote:
Sounds like a balancing problem to me, you probably need to restrict flow to some of the radiators closest to the boiler in order to allow more flow to the furthest radiator.


Unlikely with 8mm pipes. Rorchach.

Most likely would be undersized primary pipes to/from the manifolds or a tired pump.

Increasing the pipes to the radiator would help but that would be dependent on the primary pipe size


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PostPosted: Wed Nov 16, 2016 12:57 pm 
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Main pipes are 22mm. Pump is only about 3 years old and is in excellent condition ( I took it out to inspect it in the Summer when I took all the radiators out to flush them with the garden hose ).

Pump on speed 2? Historical I suppose but I am mindful of too much pressure taking water up the vent pipe. It did happen once ( by accident when the switch got moved by a child or some other means ) and I had a lovely flow of hot water up the vent and into the header tank! That was at a time with far fewer radiators though. I did have it in mind that if I did increase this one radiator to 10mm I may then need to use speed 3.

There are 3 manifolds. The original is a blind manifold with flow & return in the same unit. This is the manifold that feeds the radiator that is slow to warm up and 4 others. The other two manifolds are through types and they supply the other 5 radiators.

I have tried restricting flow to the other radiators by adjusting the lockshields but it doesn't make a lot of difference. It has to be the volume of water in this large twin panel radiator that makes it slow to warm with 8mm pipework.

I should add that once that slow heating radiator is up to temperature, the whole system works very well indeed. I'd just like this one radiator to warm a bit quicker.

Thanks for the help.


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PostPosted: Wed Nov 16, 2016 1:31 pm 
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How is that manifold connected, should be opposite ends.

Microbore requires a high speed flow restricting the valves will make it very noisy.

Pumping over is a design or system fault as the cold feed and vent should be neutral.

Increasing the pipe size will certainly get more water to the radiator, quicker, so worth a try if it's a simple task.


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PostPosted: Wed Nov 16, 2016 3:09 pm 
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thescruff wrote:
How is that manifold connected, should be opposite ends.

Microbore requires a high speed flow restricting the valves will make it very noisy.

Pumping over is a design or system fault as the cold feed and vent should be neutral.

Increasing the pipe size will certainly get more water to the radiator, quicker, so worth a try if it's a simple task.


It goes like this -

Boiler -> airjec II -> pump -> 3 port valve -> flow ( non blind ) manifold ( 5 rads ) -> blind manifold ( 5 rads )

return -

blind manifold ( return ) -> return ( non blind ) manifold -> junction with hot tank return -> magnetic filter -> boiler

All fairly conventional.

The pumping over was before the first extension was built. The system got revised at that time with the airjec II and extra manifolds. Originally the vent pipe was just off a 22mm T in the flow pipework. I don't think the pumping over is an issue any more.

The lockshields are normally fully open ( minus 1/4 turn ) and the system works fine. All rads have TRVs.

Changing the pipe to 10mm would be really easy. The pipework goes from the manifold all the way between two joists, bends down through the ceiling and down the wall to the rad. The whole project would probably only take a couple of hours. The TRV has a 15mm/8mm reducing olive and I already have a few 15mm/10mm reducer olives in my spares box so that's easy. A new 10mm lockshield would be needed. Other than the pipe, I'd also need 2 new 10mm union nuts for the manifold and 2 10mm olives.

As I have isolating valves at the pump and magnetic filter, I wouldn't even need to drain down the system.

Thanks.


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PostPosted: Wed Nov 16, 2016 3:36 pm 
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I’m sure scruff will be back later, but just a thought.

Have you checked the TRV pin has not jammed restricting the flow to the offending rad ?

Failing that your idea of increasing the pipe size to 10mm is probably worth a try and looks to be endorsed by scruff.


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PostPosted: Wed Nov 16, 2016 3:51 pm 
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I think the only problem is volume of water (large rad/small pipe) certainly a larger pipe should give a better flow rate.

The airjec should stop any pumping over, so also worth upping the speed and testing it.



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PostPosted: Wed Nov 16, 2016 3:53 pm 
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PLB wrote:
I’m sure scruff will be back later, but just a thought.

Have you checked the TRV pin has not jammed restricting the flow to the offending rad ?

Failing that your idea of increasing the pipe size to 10mm is probably worth a try and looks to be endorsed by scruff.



The radiator is working fine PLB, just not getting enough hot water quickly.


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PostPosted: Wed Nov 16, 2016 4:34 pm 
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Pipe sizes aside... a numbnuts question from a handyman..

Is the boiler up to the job of the twice extended house ?

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PostPosted: Wed Nov 16, 2016 4:41 pm 
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PLB wrote:
Have you checked the TRV pin has not jammed restricting the flow to the offending rad ?


Yes, I changed the TRV about a year ago. Partly for this reason but also because the old one had UV yellowed horribly and I couldn't be bothered to mess about with Hydrogen Peroxide etc :lol:


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PostPosted: Wed Nov 16, 2016 5:05 pm 
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thescruff wrote:
I think the only problem is volume of water (large rad/small pipe) certainly a larger pipe should give a better flow rate.

The airjec should stop any pumping over, so also worth upping the speed and testing it.


That matches my thinking - pure volume of water.

I'll try speed 3 tomorrow and see what happens although, as you say, I wouldn't expect anything untoward with the airjec in place.

Thanks


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PostPosted: Wed Nov 16, 2016 5:20 pm 
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wine~o wrote:
Pipe sizes aside... a numbnuts question from a handyman..

Is the boiler up to the job of the twice extended house ?


The boiler was changed when the first extension was put in place. The flue could no longer go through the side wall so it needed a fan flue to the back wall. It's an ageing but still working well Potterton 40e ( no kettling even in this very hard water area ). The house dates from the mid 70s and is pretty well insulated.

Obviously the 40e isn't as efficient as newer ones, but it's always a balance between fuel savings and the cost of a new boiler.


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PostPosted: Wed Nov 16, 2016 6:30 pm 
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Modern radiators would probably give a better return the a new boiler, until you have to start chucking money at it to keep it working


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