Hot water flow very low

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We had a thermal store installed, was perfect first fitted but slowly over time the hot flow has fallen especially over cold months has become increasingly worse to the point the showers etc are pathetic.
I removed the blender valve from thermal store a few months back and removed a ball of green rocks formed on the input coming from the DHWC (hot water coil) into the blender which improved things alot. Tried it again but this time is still very poor.
Basically initial flow of hot water then very low flow after that. Is this limescale build up in coil? Or a broken blender?

I was going to make up a CH pump and some pipework and Fernox DS3 to try and descale?

Any help or pointers he so much appreciated.
 
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Yep, sounds like scale to me. Descale it with DS3 as you suggest, flush out very well with clear water before reconnecting, then get yourself some scale protection. Either a water softener or a Hydroflow HS38
 
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Yep, sounds like scale to me. Descale it with DS3 as you suggest, flush out very well with clear water before reconnecting, then get yourself some scale protection. Either a water softener or a Hydroflow HS38

Thankyou muggles, i was going to plumb up a grundfos pump and 10l bucket to some pipes to connect, anything else i need to be careful of? Should that do the trick?
 
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Wear gloves and eye protection, don't spill any. DS3 is nasty stuff
 
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Is there a filter on the cold water supply to the blend valve/heat exchanger? Are the isolating valves fully open? Any chance there's an air bubble bath trapped in the pipework?
 
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It's a thermal store.... the problem is a initial surge in hot water flow and the flow then drops off ?

It's a blockage it could be in the coil but I doubt it, you have a flow restriction somewhere. Standing pressure equalises so you get that initial surge and due to the restriction the flow then drops off.

Forget about pumps.......If you removed the blending valve and rigged up a hose pipe from the hot outlet then turn on the cold do you get a good flow ...that's then eliminated the cylinder from the problem. Maybe a pressure reducing valve or the blending valve problem. You've just got to find it by a process of elimination.
I'm assuming cold flow is good.
 
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It's a thermal store.... the problem is a initial surge in hot water flow and the flow then drops off ?

It's a blockage it could be in the coil but I doubt it, you have a flow restriction somewhere. Standing pressure equalises so you get that initial surge and due to the restriction the flow then drops off.

Forget about pumps.......If you removed the blending valve and rigged up a hose pipe from the hot outlet then turn on the cold do you get a good flow ...that's then eliminated the cylinder from the problem. Maybe a pressure reducing valve or the blending valve problem. You've just got to find it by a process of elimination.
I'm assuming cold flow is good.


Hi Gasbanni thanks for your thoughts, I read this earlier on another post below the science or theory is interesting, as i often wondered why they were prone to limescale, just to add we do live in a very hard water area too. Anyway today is the day i shall try to resolve this pesky issue. Off to the plumbers shortly to get some hose connectors try first to clear out all components including the blending valve then the coil. Note i had previously removed the pressure regulator stripped and cleaned the filter that all seemed ok, as is the cold water pressure.


There are a couple of almost-unavoidable problems with heatstores, both related to temperature.

First - they ain't gonna work too well with condensing (high efficiency) boilers. Because the heatstore is held at a relatively high temperature and needs to be 'topped up' as soon as the temp drops only a small amount, the boiler will hardly ever condense. If someone knows of a heatstore that IS compatible with a steamer, let me know!

Second - there's always a bit of DHW sitting in the coil of the heatstore while all the taps are shut. This water will obviously be at the same temperature as the heatstore. now if that's above 80 it's also above the 'critical temperature' at which dissolved calcium bicarbonate in hard water changes to carbonate and precipitates-out as limescale. So the coil gets furred up. So if you've got hard water going into a heatstore, limescale will be inevitable. Some systems (but NOT AFAIK, Gledhill) fit a 'Siliphos' inhibitor on the cold supply as standard.
 
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OK exciting update!!

So to recap our hot water was really poor, not very hot and no flow or pressure.

Of course being a skin flint and tight on money decided after descaling the mixer valve and some help from people here deduced it MUST be the DHWC.

I bought a 2nd hand new Grundfos pump borrowed some hoses off a very generous local plumber merchant who's powerflush machine was knackered so i used them.

Knocked up a very rudimentary system with an old cider brewing bucket added some water to test.

I just couldn't get the pump to prime properly, why??? The water from the return pipe back to the bucket was dribbling out.

Wait a minute ive already forgotten why im doing this, i guess it reaffirmed i was doing the right thing.

Dropped in a kilo of DS3 into a 10litre bucket of v hot water, and let the pump start sucking it up. Few minutes later spluttering..

Then wow 5 mins later the water is flowing out the other end just as i expected it to be. Fking pleased as punch i am!!

So for the cost of pump off classifieds and a few fittings and Ds3 cost me £40. That's not bad.

I shall add a few pics shortly for you to laugh at my leaf robinson contraption but fk me it worked!!

In the morning im back there to buy what muggles recommended and the plumber merchant agreed as a wise choice a Hydroflow HS38. Just out of interest anyone else installed one of these? Good results? When i read on here and other places i see alot of people comparing these to snake oil. (no offence muggles just inquisitive)

What a good evenings work.
 
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