westf27
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| posted on 16/3/12 at 05:08 PM |
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domestic hot water....low pressure
Got low pressure..well after a few seconds as normal the flow drops off to very slow rate.The boiler is in the kitchen and upstairs is the hot
tank,motorised valves and two pressure vessels.There is a mains water stopcock which feeds via a filter into the hot tank via some sort of pressure
valve which is set at 3 bar.I was thinking the pressure valve is probably faulty ?are they adjustable ? any ideas
was wondering whether the mains water feed comes via the boiler or not
[Edited on 16/3/2012 by westf27]
[Edited on 16/3/2012 by westf27]
555
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daniel mason
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| posted on 16/3/12 at 05:27 PM |
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is it a modern pressurised cylinder or an old gravity fed one?
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westf27
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| posted on 16/3/12 at 05:31 PM |
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its a pressurised cylinder
555
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martinq357
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| posted on 16/3/12 at 07:25 PM |
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If the mains pressure is ok out of the cold tap, i'd start with the filter before the refeif valve - could have blocked or broken up and be
impeding the flow??
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motorcycle_mayhem
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| posted on 16/3/12 at 08:25 PM |
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OK... I recently replaced the diverter valve and diaphragm on my Mother-in-Laws aged Halstead boiler.
The diaphragm had a hole in it from wear (not uncommon it seems), so it wouldn't lift the valve all the way open when hot hot water was
demanded... eventually it wouldn't lift at all, no hot water. Simple job, I could have simply replaced the diaphragm, but everything was so
corroded when I dismantled it - I went for rhe complete assembly. Not expensive.
I also wipped the heat exchanger out at the same time, pretty choked with salts. A few hours with an acid flush, it was much better.
What isn't Locost is to get the 'experts' in. The scum simply seem to want to swap boards and charge old people (hence the reference
to Mother in Law) vast amounts of money - leaving the boiler/whatever with the same malfunctions.
I apologise to the honest plumber/boiler guys out there.
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Not Anumber
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| posted on 19/3/12 at 09:52 PM |
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i used to be a plumber, which type of heating system do you have ?
I'll outline the 3 basic types of heating & hot water systems.
Combi Complex but compact boiler where the primary side runs pressurised (with a pressure vessel normally inside the boiler on the primary side).
Domestic hot water is heated just as it's needed within a small heat exchanger inside the boiler. This heat exchanger is effectively all there
is to the secondary circuit as theres no external hot water storage vessel. Clean cold water is taken into this, heated through the heat exchanger and
onwards to the hot taps. Advantages, easy to install, takes up less space, hot water always available. Disadvantages, hot tap may have to run for a
minute until boiler starts to heat up, only enough hot water pressure for 1 or 2 taps at the same time..
Regular boiler, regular hot water storage cylinder. The primary side is normally fed via a (dirty) tank in the loft (and circulated round the heating
system by pump) but this could equally be pressurised instead to avoid having to fit a tank in the loft, in which cae there would be a pressure vessel
and a filling loop on the primary side. The boiler is a straightforward unit -one primary circuit with just a flow and a return pipe. A lagged,
copper hot water cylinder is also part of the primary circuit, seperately switched from the radiators by a solenoid valve and timer. The secondary
side of the hot water cylinder has a water inlet at the bottom (fed from a higher, semi clean, tank) and an outlet at the top which goes to the hot
taps. Advantages; will cope better with 2 or more hot taps open at once. Disadvantages, space, more pipework, have to wait a while for domestic hot
water if boiler hasn't fired up for a while.
Regular boiler with Sadia Meagaflo (or similar) hot water cylinder. Similar to a conventional set up but this time the hot water cylinder is more
substantial and it's secondary side is designed to be fed from the mains to give increased hot water pressure - great if you want several taps
open at once. It's also common for the primary side to be run pressurised with a filling loop and pressure vessel.
If it's the 3rd type of system which i think it may be from what you say then the main thing is to make sure that the stop valvethat feeds cold
water from the mains into the Megaflow is fully, or nearly fully, open and the same with it's outlet valve
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westf27
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| posted on 20/3/12 at 08:54 AM |
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its the sadia megaflow type.The mains feed to the prv is fully open,havent seen an outlet valve but will check again.Does the mains water feed come
directly from the main or via the boiler ? Is there anything external that would affect the opening of the prv to give good flow.I am assuming that
the flow of hot should be similar to that of the cold.
[Edited on 20/3/2012 by westf27]
555
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MkIndy7
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| posted on 20/3/12 at 09:05 AM |
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Some PRV's are adjustable, others are not try moving the top of it and see nothing to loose it may work better at a different pressure.
From your description of how it has the correct standing pressure i.e when you first open the tap, but not the correct running pressure and all
filters are clear I'd say it was the PRV.
If your mains pressure isisn't very high and the Safely valves are marked as 6bar you could probably remove the PRV and replace with a straight
bit of pipe as A TEST only!.
This leg of pipe work comes straight from the cold water main it has nothing to do with the boiler setup.
Just seen the pic, yes that type is adjustable the green indicator at the top should move to indicate its set pressure as you spin the black top of
the valve.
[Edited on 20/3/12 by MkIndy7]
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westf27
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| posted on 20/3/12 at 12:49 PM |
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well thanks for all the help guys only hope I can report back a success
555
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