Radiators stopped getting hot - everything appears to be working.

[PolkadotFish]

Assuming the heat store is "vented" then its a bit surprising that there isnt a vent of some sort (even manual) from the top of the store.

It has a bottle air vent.
It doesn't collect much gas (being near the bottom of the system). But I do vent it periodically. I do not believe this is the issue.

Do you get any air from the rads when you vent them even with LPG boiler on?.

Not normally.
I've had a few issues in the past (now largely solved) that lead to air or gas in the system. This conveniently collected in one particular radiator (downstairs!) that could easily be bled away.
There's no sign of collecting gas or air locks anywhere in the house system - it all works fine on the LPG.

It's possible there's an air lock between the house and the heat store, but it's not obvious where - all the above ground pipes travel horizontally or vertically upwards from the lowest point without any obvious places for gas to collect.

The underground pipe is basically horizontal. I suppose there could be a long arc? How would I check?

There are drain points at the lowest point in the cellar (~7.5m head from F&E tank). I've timed how long it takes to fill a 2 litre jug, without any pumps on, to check for obstructions in the pipes between the heat store and the heating system in the house:
The quickest (F&E tank > cellar drain ~35m) around 4 seconds.
The longest (F&E tank > cellar > heat store > cellar drain ~105m) around 30 seconds.
The timings are similar between flow and return pipes.

I'm not sure how useful these numbers are though.
Obviously coming 35m straight down the house is quicker than travelling 35m down and 70m horizontally. But 15s/litre seems pretty slow to me.
But I've not got any numbers to compare them to.

Can you post a photo of the details on the heat store labels.

Do you mean the heat store data plate?

By unrestricted I mean that there is no blockage in this pipe, this can be quite common where its teed into the system, you could drain off say 5L or so and see if the F&E cistern starts refilling rapidly which will prove it clear.

I've partially drained the system several times recently (see above. Also replaced leaking pump valve). It always fills quick enough.

Is it teed into the flow or the return piping?.

Shortly before P1. So return?

If the Wilo set to C3 at 7.9M still only results in very poor circulation on bypass then it logicall has to be a restriction somewhere or air somewhere,

I think so.

the condition of the F&E cistern if you look into it will give a good indication of a clean/dirty system.

The cistern water is clear. I've recently replaced a radiator bleed valve, I've drained water out of the system from various points, I drain the Fernox TF1 annually.
Apart from the small debris collected by the magnet, there's no sign of sludge etc. Drained heating water appears largely clear (certainly settles clear).

 

[Johntheo5]

There are drain points at the lowest point in the cellar (~7.5m head from F&E tank). I've timed how long it takes to fill a 2 litre jug, without any pumps on, to check for obstructions in the pipes between the heat store and the heating system in the house:

The quickest (F&E tank > cellar drain ~35m) around 4 seconds.

2L/4secs=30LPM=1.8m3/hr. A flow of 1.8m3/hr through 35M of 28mm piping should only require a ~ head of 1.7M, a head of (if) 7.5m should give a flowrate of ~ 4.0m3/hr

The longest (F&E tank > cellar > heat store > cellar drain ~105m) around 30 seconds.
The timings are similar between flow and return pipes.

This is important, what is the ~ elevation from the bottom of the F&E cistern to the actual drain point?

I'm not sure how useful these numbers are though.
Obviously coming 35m straight down the house is quicker than travelling 35m down and 70m horizontally. But 15s/litre seems pretty slow to me.
But I've not got any numbers to compare them to.

Do you mean the heat store data plate?

Yes.

I've partially drained the system several times recently (see above. Also replaced leaking pump valve). It always fills quick enough.

that would appear to rule out any restriction in the cold feed.

Shortly before P1. So return?

I think so.

The cistern water is clear. I've recently replaced a radiator bleed valve, I've drained water out of the system from various points, I drain the Fernox TF1 annually.
Apart from the small debris collected by the magnet, there's no sign of sludge etc. Drained heating water appears largely clear (certainly settles clear).

 

[PolkadotFish]

Some of the information you want below, plus some extra in case it's useful.

Just a reminder that nothing is to scale and there might be some mistakes because of dyslexia, lack of knowledge etc. Please check anything that might be important.

 

[Johntheo5]

"The longest (F&E tank > cellar > heat store > cellar drain ~105m) around 30 seconds.
The timings are similar between flow and return pipes."

This the one I'm mostly interested in, just now, the reason I'm interested is that a flowrate of 2L/30s, 4LPM, 0.24m3/hr is very similar to the pumped bypass flowrate.
So, can you you highlight this on any schematic to show its run and the ~ elevation from the F&E to the drain off point.

 

[Johntheo5]

This is where I calculate the head loss/flowrates etc.

Friction Loss Calculator - National Pump & Energy

Calculate your efficiency losses due to friction in your system pipeline with NPE's easy-to-use Friction Loss Calculator.

www.nationalpump.com.au

 

[PolkadotFish]

"The longest (F&E tank > cellar > heat store > cellar drain ~105m) around 30 seconds.
The timings are similar between flow and return pipes."

This the one I'm mostly interested in, just now, the reason I'm interested is that a flowrate of 2L/30s, 4LPM, 0.24m3/hr is very similar to the pumped bypass flowrate.
So, can you you highlight this on any schematic to show its run and the ~ elevation from the F&E to the drain off point.

I opened/closed various valves to test the flow through the 4 options from the F&E to the drain taps in the cellar:
F&E to flow pipe to cellar.
F&E to return pipe to cellar.
F&E to flow pipe to heat store to cellar.
F&E to return pipe to heat store to cellar.

The two direct to cellar were similarly short.
The two via the heat store were similarly long.

I gave your the shortest and longest times.

 

[Johntheo5]

If I'm interpreting your numbers correctly then one test gives a flowrate of 30LPM, 1.8m3/hr, through 35M of pipe with a 7.5M head, the pipeloss table shows that a pipe with a 18.5mm ID will flow this, (28mm pipe is I think nominally 25mm ID), using 18.5mm ID then 150M of pipe should flow 13.8LPM, 0.83m3/hr, not great, but will give a rad(s) output of 14.5kw at a dT of 15C or 19.3kw at a dT of 20C.

But another test gives a flowrate of 4.0LPM, 0.24m3/hr through 105m of pipe (also through the store) with a 7.5M head, this now gives a pipe ID of only 10.7mm and a flowrate of 3.3LPM, 0.2m3/hr through 150mm of pipe which is what you were seeing with the pumps on??.

The difference in these two tests, apart from pipe lengths is that the water flows through the store in the second test but one would think that the pressure loss through this should be far less ( a fraction) than the equivalent length of pipe?.
Maybe be worth checking the inlet and outlet on the store in case of any scale build up, especially the outlet.

Anyway, stick in the bit of pipe and see what happens with the Wilo.

 

[PolkadotFish]

The difference in these two tests, apart from pipe lengths is that the water flows through the store in the second test but one would think that the pressure loss through this should be far less ( a fraction) than the equivalent length of pipe?.

Indeed!

Maybe be worth checking the inlet and outlet on the store in case of any scale build up, especially the outlet.

I'm not sure how to do this?

There won't be any scale. We don't have any significant dissolved minerals in our water.
Removed pipes and fittings often show a very thin black coating of something that wipes off, but it doesn't build up.

I can only imagine something has got into the system and partially blocked something?
There have been occasional flakes of metal (I presume from the inside of the furnace heat exchanger).

When I was swapping pumps around, I did put P2 & P3 on backwards and run then for a while in the hope it might dislodge something. But it didn't make a difference.

Anyway, stick in the bit of pipe and see what happens with the Wilo.

I'm not easily able to do this either.

I was hoping to find fittings to allow me to connect the two pump valves together (in place of the pump). But it's going to cost at least £50 to buy the fittings locally.

I could take the pipe valves off, but that would involve draining down a lot of heating water (and replacing the heating water treatment chemicals).

Given that the pump housing and veins aren't clogged, and I didn't have any improvement when I put the Wilo in the P3 position, I'm expecting to get the same/similar result with pipe or pump.

I think I need some way to narrow down the location of the restriction, then I can drain down that section as necessary to clear/repair.

Any techniques for hunting a restriction?

 

[Johntheo5]

Indeed!

I'm not sure how to do this?

There won't be any scale. We don't have any significant dissolved minerals in our water.
Removed pipes and fittings often show a very thin black coating of something that wipes off, but it doesn't build up.

I can only imagine something has got into the system and partially blocked something?
There have been occasional flakes of metal (I presume from the inside of the furnace heat exchanger).

When I was swapping pumps around, I did put P2 & P3 on backwards and run then for a while in the hope it might dislodge something. But it didn't make a difference.

I'm not easily able to do this either.

I was hoping to find fittings to allow me to connect the two pump valves together (in place of the pump). But it's going to cost at least £50 to buy the fittings locally.

I could take the pipe valves off, but that would involve draining down a lot of heating water (and replacing the heating water treatment chemicals).

Given that the pump housing and veins aren't clogged, and I didn't have any improvement when I put the Wilo in the P3 position, I'm expecting to get the same/similar result with pipe or pump.

Yes, I think that's a reasonable assumption since I think you tried both UPS pumps in the P2 position and the Wilo is brand new so the combined head should result in a reasonable flow.

I think I need some way to narrow down the location of the restriction, then I can drain down that section as necessary to clear/repair.

Any techniques for hunting a restriction?

 

[Johntheo5]

What about the comment I made in post #37 where the 35M test woud indicate that a flowrate of ~ 1.0m3/hr might be possible with 150M but the "105"M test gave a completely different picture, apart from the length the store was (if) also being circulated?.,

 

[PolkadotFish]

I've found the problem!

Timing the flow from the mid-point in the cellar was partially useful (it confirmed a restriction) but it wasn't clear where it was.

So I made pairs of valves with a drain in between so I could check each quarter separately.

This showed that the restriction was between the cellar and the heat store on the hot-flow-to-house side.

The cellar junction is right next to the underground pipe (not expecting a restriction underground), so the problem must be at the heat store end.

By directing the flow in various ways I was confident that the tank outlet wasn't blocked.
That meant I could check all the fittings from there on without having to drain down the system.

Everything seemed fine. There was one final gate valve near where the plumbing joined the underground pipe - that was the last fitting to check.

I removed the insulation from around it. There was a bit of corrosion on the pipes. I removed the valve - it was fine!

With that valve removed I opened the valve from the tank - only a trickle of water! So confused.

I pulled more insulation off and found it - a one way valve is didn't know was there.

took it off - it's partially jammed.

So - do I need to replace it?
What's it for? Can I bypass it?

Is there likely to be another one on the return?



@Johntheo5 Thanks for all your help and time.

 

[Johntheo5]

What exactly is it?, a simple, spring loaded non return valve or something else?

Can you indicate on the (a) schematic where its installed

 

[PolkadotFish]

I think it's a normal non-return valve. A diaphragm and a spring?

 

[PolkadotFish]

It's cost over £500 in LPG so far!
I hope there isn't another one buried somewhere.

 

[Johntheo5]

Presume its installed the right way round!,
It may be required to stop the LPG boiler (when on) pumping water into the top of the store and back through the biomass boiler and even though unlikely up through the biomass boiler vent, so have a good look before (if) removing it., if its a swing check valve then I would be inclined to just renew it as these have little or no head loss.