Power flush heat store advice

[speccy]

Ok maybe left this a bit late but here goes.

I have a thermal(heat) store in our CH system which supplies mains DHW. Ive noticed as of late the Hot water pressure/flow quite low normally descaling the input from the DHWC primary coil (a gauze filter on the mixer valve) fixes the issue.
However it seems as of late pressure still low which leads me to think the coil is getting blocked, water in this area is hard. Can the mixer valves fail and cause this issue or do you believe it's the domestic hot water coil?

I also have an issue with a few rads never getting warmer than about 35degs some are piping hot.

My thoughts were to hire one of these to flush the DHWC in the heat store and then switch it to flushing the CH system. Yes i would pay someone 500+ to do it proffessionally if i had the money but im out of work and poor. And i do have reasonable plumbing knowledge and ability.

https://www.hss.com/hire/p/central-heating-flusher

Any thoughts very much appreciated.

 

[oldbuffer]

1. Some radiators never getting warm while others are hot suggests to me that:
1a. The system needs balancing.
1b. The cool radiators are on an extension to the system with inadequately sized pipes.
2. Power flushing is normally done to remove "sludge" from central heating systems. This sludge is mostly magnetite, not lime scale from hard water.
3. If you are going to power flush to remove lime scale, make sure:
3a. You use and appropriate chemical.
3b. The chemical is suitable for use with the power flushing machine you are using.
4. The coil is essentially a heat exchanger. There are therefore three possibilities with respect to lime scale:
4a. The hot side (the body of water in the store) has scaled up, preventing the heat reaching the exchanger.
4b. The cold side (the water being heated) has scaled up, preventing heat transfer and also reducing flow.
4c. Both 4a and 4b.
5. In your situation I'd try descaling the hot water circuit first by running a descaling agent such as Fernox DS 3 through the cold water side of the heat exchanger. You will need a pump of some sort, with reversing facilities, to do this, but it doesn't need a full scale power flush pump. Something like a Decalomat (try Ebay ?) would do. You will have to break into the domestic hot water circuit somehow to connect it. If you are in West London I've got one you could borrow.
6. If that doesn't work, only then would I try a full scale power flush.
7. If you want a good guide to power flushing, look at the Kamco web site.

 

[oldbutnotdead]

It'll be worth stripping the blending valve & give the innards a good clean before getting the chemicals in. Is there another inline filter before the valve? Or a backcheck valve clogged up?
The rads- upstairs or downstairs? Tiny pipes?

 

[speccy]

First of all thankyou so much for the offer but i am way down deep south west.

1. Some radiators never getting warm while others are hot suggests to me that:
1a. The system needs balancing.
1b. The cool radiators are on an extension to the system with inadequately sized pipes.
2. Power flushing is normally done to remove "sludge" from central heating systems. This sludge is mostly magnetite, not lime scale from hard water.

Last year when i fitted a Ladomatt i did first 'flush' some of the system through by leaving the mains filler on, and a hose from the drain cock from the last rad in the circuit (filler sits about halfway in middle of circuit) into the garden until it ran from black to clear and removed 4 of 11 rads drained some black sh't out of them. Not sure if that's helped much.

1. Some radiators never getting warm while others are hot suggests to me that:
4. The coil is essentially a heat exchanger. There are therefore three possibilities with respect to lime scale:
4a. The hot side (the body of water in the store) has scaled up, preventing the heat reaching the exchanger.
4b. The cold side (the water being heated) has scaled up, preventing heat transfer and also reducing flow.
4c. Both 4a and 4b.
5. In your situation I'd try descaling the hot water circuit first by running a descaling agent such as Fernox DS 3 through the cold water side of the heat exchanger. You will need a pump of some sort, with reversing facilities, to do this, but it doesn't need a full scale power flush pump. Something like a Decalomat (try Ebay ?) would do. You will have to break into the domestic hot water circuit somehow to connect it. If you are in West London I've got one you could borrow.

Id go for 4B as the flow is definitely reduced, when we first had this system installed (late 2018), summer or winter turning on the hot or cold from mixer in kitchen wasn't that much difference, its very noticeable now.
Couldn't find a Decalomat anywhere on ebay/gumtree/fb classifieds found a Rothenberger rocal but they're about 90quid(and the only one is collect in person in Manchester!) the power flush is 75 to hire so may have no choice.

 

[speccy]

It'll be worth stripping the blending valve & give the innards a good clean before getting the chemicals in. Is there another inline filter before the valve? Or a backcheck valve clogged up?
The rads- upstairs or downstairs? Tiny pipes?

Hi there thanks for your thoughts, nothing else inline, oh wait, apart from this which i gather regulates the pressure into the cylinder (set to 3.35 i think) as this feeds the cold and hot mix into the blending valve.

 

[muggles]

Hi there thanks for your thoughts, nothing else inline, oh wait, apart from this which i gather regulates the pressure into the cylinder (set to 3.35 i think) as this feeds the cold and hot mix into the blending valve.

....and has a filter inside it

 

[oldbutnotdead]

Looks pretty similar to this one, check the Maintenance section

 

[festive]

Thankyou people ok looked up my valve its the one without a strainer/filter. Going to follow this detail first as per technical papers.



Just an observation it's saying unscrew the calibrating screw is this not the grey nob on top do i flip a cap off and unscrew?

 

[oldbutnotdead]

You should just be able to turn the knob anticlockwise unless the screw under the knob acts as a lock (to prevent accidental adjustment)

 

[speccy]

You should just be able to turn the knob anticlockwise unless the screw under the knob acts as a lock (to prevent accidental adjustment)

OK for anyone who cares you just wind back the grey knob so the pressure is back to 0, then undo thewholeunit. i removed the pressure regulator clean as a whistle it was.



Removed the mixer valve, seemed to have some remnants of hard water or limescale in there as i could hear quite a bit of fizz when i dipped it in descaler. Left it in the jug to descale for a while. Shall refit this shortly and reconnect see if this makes a difference. EDIT to say this made no difference either.

Otherwise it's time to flush the DHWC with the appropriate limescale remover.

As i can't find a flushing pump local i saw this, could be a viable option as i've seen this exact style pump for sale local albeit the smaller version at 9000 litres per hour ? Would this do the job? Fill it with Fernox DS40?