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Author Topic: micro bore gas central heating  (Read 6484 times)
regen
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« on: February 12, 2015, 07:39:01 AM »

I have a house with an old (probably more than 15 years) microbore central heating system powered by a potterton metaheat electronic gas boiler. this runs 13 rads over a floor area of 110m2. All the upstairs rooms get too hot whilst downstairs is generally still chilly. None of the rads have thermostatic valves fitted. Would fitting these help to balance the system or is there a cheaper way (The microbore valves are about 15 plus each)

Regen
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Countrypaul
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« Reply #1 on: February 12, 2015, 07:52:32 AM »

I have a house with an old (probably more than 15 years) microbore central heating system powered by a potterton metaheat electronic gas boiler. this runs 13 rads over a floor area of 110m2. All the upstairs rooms get too hot whilst downstairs is generally still chilly. None of the rads have thermostatic valves fitted. Would fitting these help to balance the system or is there a cheaper way (The microbore valves are about 15 plus each)

Regen
Fitting them shoudl result in a more comfortable upstairs and reduced gas usage. If the radiators downstairs are too small/gunged up/restricted then it won't help warming downstairs though.
Have you tried BES for the valves, looks like about 6.50 upwards which would make a significant difference is you're after a cheaper option.

http://www.bes.co.uk/products/115.asp#21489
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Antman
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« Reply #2 on: February 12, 2015, 08:12:32 AM »

Regen

Not sure if you mean 10mm or 8mm microbore. 8mm is a PITA as it blocks up too easily with sludge and could be an issue especially if no inhibitor in the system.

Whilst fitting TRVs, change the lockshields to a type with built-in drain-off. This will enable you to flush every flow and return pipe separately and identify if you have flow issues. They also make it easy to drain an individual rad to remove for decorating.

Honeywell VT115/VT117 are good although 12 upwards - never had one of these stick yet in 15 yrs of using them. Tried various other makes with varying degrees of longevity. Pegler Terrier IIs can tend to stick after a few years but can usually be freed off easily w/o drain down.

Antman
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Fintray
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« Reply #3 on: February 12, 2015, 10:19:21 AM »

It makes no difference to balancing the system whether there are thermostatic valves fitted as you should open the flow valves fully and then restrict the flow using the lockshields. Generally start off with the radiator furthest from the boiler with the lockshield wide open and then throttle back the remainder more as their distance from the boiler pump decreases and take it from there.
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regen
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« Reply #4 on: February 12, 2015, 10:35:38 AM »

Thanks for the replies- still getting my head round the system. Unfortunately it looks like it may be the 8mm system but good to know there are some reasonably priced valves out there- thanks for the links. At the moment all the rads get very hot so at least no blocked pipes yet! At the moment my gut feeling is that I should fit the thermostatic valves to the rads if only to reduce the gas usage and allow lees heat in the rarely used parts of the house.

Regen
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pj
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« Reply #5 on: February 12, 2015, 10:47:54 AM »

It makes no difference to balancing the system whether there are thermostatic valves fitted as you should open the flow valves fully and then restrict the flow using the lockshields. Generally start off with the radiator furthest from the boiler with the lockshield wide open and then throttle back the remainder more as their distance from the boiler pump decreases and take it from there.

On the contrary, if you have thermostatics on every radiator (with a bypass somewhere) then there is no need to balance the system - set the lockshields fully open everywhere. The system will self balance as the rooms warm up, with maximum heat flow available to achieve this. The only downside is if the house has got really cold, some rooms will heat up slightly quicker than others due to the imbalance, but it will soon settle down.
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Fintray
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« Reply #6 on: February 12, 2015, 01:14:55 PM »

None of the rads have thermostatic valves fitted. Would fitting these help to balance the system or is there a cheaper way (The microbore valves are about 15 plus each)

Regen

PJ Regen asked if fitting these would help balance the system (which they won't) or is there a cheaper way (yes balance the system with existing valves).  Smiley
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baker
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« Reply #7 on: February 12, 2015, 02:30:05 PM »

you mean potterton neta heat
is it the old type with the brown bottom metal case?
baker
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Quakered
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« Reply #8 on: February 12, 2015, 02:48:57 PM »

When I installed our central heating 40 years ago you could get little compression fittings that fitted inside the half inch TRV compression fitting to give a nice neat installation. I used 10mm micro bore throughout and the only problem I haver had in those 40 years was when I drained down the system to add another rad and did not bother in add inhibitor when refilling. This resulted in a couple of blocked rads. A nice little summer's day job to drain down again, take rads odd the wall and flush them in the garden with the hose and flush out the microbore to the rads (very carefully). Then added the inhibitor and no more problems!

I found this converts on the web http://wiki.diyfaq.org.uk/index.php?title=Fitting_TRVs_to_Microbore no sure if they are any good.
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regen
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« Reply #9 on: February 12, 2015, 03:13:58 PM »

Insert Quote

"you mean potterton neta heat
is it the old type with the brown bottom metal case?
baker"

Potterton neta heat electronic with a grey/black back and bottom case and a cream one piece front and side case which I guess can be removed by qualified fitter.

Regen
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« Reply #10 on: February 13, 2015, 01:23:52 AM »

Regen, as others have said microbore whether 8 or 10mm is a PITA for blocking/clogging etc. Microbore systems do need careful balancing when no trvs are fitted as the resistance of the pipework varies greatly on different lengths and due to the nature of the systems the rads tend to be each one long run from a manifold or reducing fittings positioned in a certain spot. Downstairs rads will usually be a longer circuit and have a bit harder time of it. If you are going to drain down to put trvs on (and you really should have trvs) then put a tub of cleaner in for a few days before the big drain down.

I use danfoss rasc2 which you can get in a 8-10mm version, it has reducing fittings which go in place of an ordinary olive, though the Honeywell vt117 are very good also. Regardless of what valve you opt for, on microbore systems you tend to have to cut pipework to get rid of old nuts and olives and solder new bits on for the new valve. Leave the rad in the room with the wall stat without a trv on, hopefully you have a bypass on the system to maintain a minimum flow through it all.

As for balancing, it is needed (and Fintray describes it perfectly) on all systems which have trvs fitted but it is not as crucial to be absolutely exact as on systems without trvs due to the nature of trvs being able to shut off when they reach the required temperature which then has the effect of diverting more flow/heat to other places. If you are open vented then just be careful not to shut everything down too much as you might easily end up with pump over into the header tank.
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dhaslam
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« Reply #11 on: February 13, 2015, 10:22:09 AM »

It would be  better to split up the system into two or more circuits.   It would require one or two  new manifolds and valves for each circuit.   The circuits could then be controlled  separately, preferably with  time and temperature controls with a suitably placed thermostats.    Radiator valves are not very satisfactory,  they tend to get stuck  in the off position after the summer  and are not very accurate. The worst thing about  radiator valves is that everone seems to just turn them up to the highest setting.
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regen
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« Reply #12 on: February 14, 2015, 07:59:09 AM »

Thanks for all the info. I had to have a new landlord cert on the gas boiler so I got a company to quote for a new boiler and surprise, surprise-  that after servicing it as well the conclusion was that there was nothing wrong with it so leave well alone. I wanted to put a wbs in the lounge but the installation cost plus the fuel cost if you buy it in and its in a smokeless zone really makes it uneconomical. Fortunately there is a gas point adjacent to the fireplace and although its never been used it is still functional so a small gas fire will sort out the local lounge heating. I will have a go at rebalancing the rads but will leave fitting any trvs until the warmer weather when the system can be flushed and cleaned properly.
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 Sheep, poly tunnel and approx 80 sq m of raised veg beds.
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