Radiators stopped getting hot - everything appears to be working.

[PolkadotFish]

Everything works normally with the backup LPG boiler.

When the heat is supplied form the Heat Store, the supply pipes get hot, but the radiators only get a bit warm upstairs and stay cold downstairs.

System has otherwise worked ok for over 10 years.

I have checked all parts of the system that I can, but can't identify a fault. Currently spending a fortune on LPG!

Basic layout below.

Either the LPG boiler and Pump 1 are running (everything works)
or Pump 1, 2 and 3 are running.
Motorized valves shut the other heat source.

How can I identify the fault?

 

[cross thread]

Are the zone valves on the heat store opening

 

[PolkadotFish]

Yes.

I have checked that they are correctly operating when called and that the valves are working.

I have replaced all the zone valve heads and one of the valves over the last 10 years.

Actually the zone valve to the heat store is normally open - when the LPG is called it closes the zone valve to the heat store and opens the LPG one.

There is also a bypass valve that returns the cold water (sitting in the pipes underground) back to the heat store until the hot water arrives, then that closes and Pump 1 starts.

The flowmeter is reading 0.2 - 0.4 m²/h coming to the house, going through the bypass valve then back to the heat store.
Once it's hot and P1 joins in to push it round the house the reading is 0.1 - 0.3 m²/h

 

[Mike13]

well, if it is flowing via p1 and the radiators are staying cold, then it is pushing fluid into the 200 litre hot tank which is already warm, I suspect the zone valves are not fully switching on demand.
You might need to make a fully exact copy of the plumbing for your own use and double check which valves are pointing fluid and where it is flowing in each mode of operation. It seems you know it is flowing a reasonable amount from the heatstore, what is the return temperature in each mode (heatstore& LPG), that might give you a clue as to where the hot water is actually going.

 

[PolkadotFish]

The hot water tank isn't getting hot enough either.

When running on LPG I can feel the pipes are too hot to hold onto heading into the radiators and/or the hot water tank. The return from either the radiators or hot water tank feels very warm.

When running from the heat store I can feel the pipes are too hot to hold onto heading into the radiators and/or the hot water tank. However, both the return flows feel cool or cold.

"You might need to make a fully exact copy of the plumbing for your own use and double check which valves are pointing fluid and where it is flowing in each mode of operation."

I'm not sure what you mean by this, can you elaborate please.

I don't know if the flow rate is appropriate. The pump curves for P1 suggest it's operating around 2m³/h so possibly the flow rate from the heat store is bringing warm water to P1, but not fast enough to keep up with the circulation around the house?

 

[Johntheo5]

How does the LPG heat the heat store?, pump P3 is pumping against the LPG flow, also P2 should be pumping into the heat store return?

 

[PolkadotFish]

The Heat Store is heated by a biomass boiler.

When the LPG boiler is on only P1 runs.
Heat from the LPG boiler doesn't go to the heat store.

 

[Johntheo5]

Is the stored water pumped directly through the rads (and indirectly through a coil in the HW cylinder)? , why the need for 3 pumps?.

 

[MeldrewsMate]

Have you determined whether pumps P2 and P3 are running, and if the by-pass valve is closing once the long primary pipes are hot/warm? It seems odd that the flowrate is lower when 3 pumps are running, rather than 2.
It is also clear that pump P1 has enough grunt to circulate through the rads on its own, however if the LPG valve is not shutting (you said it is NO and powers to close) then the flow from P1 will be shunted around the LPG boiler and REDUCE the heatstore flow.

Have you felt the LPG boiler pipework when on heatstore, to see if they get hot/warm?

 

[MeldrewsMate]

Is the stored water pumped directly through the rads (and indirectly through a coil in the HW cylinder)? , why the need for 3 pumps?.

Probably because there is a 140 metre run between the heatstore and the house.

 

[Johntheo5]

Can you post the pump(s)make/model/mode/setting and the pipe diameter and material.

 

[PolkadotFish]

Is the stored water pumped directly through the rads (and indirectly through a coil in the HW cylinder)?

Yes.

why the need for 3 pumps?.

70m (140) pipe run with 5.5m head.

Have you determined whether pumps P2 and P3 are running,

They are. But I'm not sure they're running at full spec.

and if the by-pass valve is closing once the long primary pipes are hot/warm?

The bypass valve closes. After a while, the closed side cools down.

It seems odd that the flowrate is lower when 3 pumps are running, rather than 2.

Indeed.

It is also clear that pump P1 has enough grunt to circulate through the rads on its own, however if the LPG valve is not shutting (you said it is NO and powers to close) then the flow from P1 will be shunted around the LPG boiler and REDUCE the heatstore flow.

The heat store, as the primary source, has an NO valve and the LPG valve is NC. Both valves are operated when the LPG boiler is called. Both valves are working.

Have you felt the LPG boiler pipework when on heatstore, to see if they get hot/warm?

I have - they don't.

Can you post the pump(s)make/model/mode/setting and the pipe diameter and material.

 

[PolkadotFish]

Can you post the pump(s)make/model/mode/setting and the pipe diameter and material.

I forgot the settings:
P1 = CC 2 or 3
cc1 makes the boiler overheat.
I've tried different modes, but makes no obvious improvement.

P2 & P3 on setting 3. Again, changing them doesn't make anything better.

 

[Johntheo5]

Just making a few assumptions here to get a feel of the syatem, you can correct them.

assuming 28mm piping has a ID of 25mm and a total length allowing +10% for bends etc of 154M
assuming that the installed rad output is 30kw
A rads dT of 15C requires a flowrate of 28.7LM, 1.72M2/hr, 154M of 28mm piping has a dP of ~ 6.9M, add say 1M for dP across the rads = total pumping head of 7.9M.
A rads dT of 20C requires a flowrate of 21.5LM, 1.29M2/hr, 154M of 28mm piping has a dP of ~ 4.1M, add say 1M for dP across the rads = total pumping head of 5.1M. The UPS3 pump below is a very powerful pump and even on its own should have no problem in circulating 1.29m3/hr (rads dT 20C) as it will supply this flowrate at 6M on CC3.

Can you find the pump curves for the other two pumps and post them.

I would suggest shutting the inlet/outlet isol valves on each pump and remove its head, give the pump ports a quick backflow from each side to prove the pump ports clear and push a tiewrap through the impeller vanes to prove clear.
Also that UPS3 has a very disproportionate failure rate and unfortunately does not display the power in watts, a very useful aid on any A rated pump, most makes now do and also didplay the flowrate.

What is the output of the LPG boiler and its minimum output if it modulates? and its ~ distance from the rads.

Is the boiler heat only with no internal pump?

 

[PolkadotFish]

assuming 28mm piping has a ID of 25mm and a total length allowing +10% for bends etc of 154M

This is just the run between the heat store and P1. Not the runs from P1 to the rads.

Do I need to measure the pipe runs in the house?
Do you need to know the lengths broken down by the different pipe diameters?

assuming that the installed rad output is 30kw

Is it useful to measure the rads area²?
An online room calculator said I needed over 50kW!

A rads dT of 15C requires a flowrate of 28.7LM, 1.72M2/hr, 154M of 28mm piping has a dP of ~ 6.9M, add say 1M for dP across the rads = total pumping head of 7.9M.
A rads dT of 20C requires a flowrate of 21.5LM, 1.29M2/hr, 154M of 28mm piping has a dP of ~ 4.1M, add say 1M for dP across the rads = total pumping head of 5.1M.

I think we might need to re-calculate these for the house pipe lengths? Or have I misunderstood?

The UPS3 pump below is a very powerful pump and even on its own should have no problem in circulating 1.29m3/hr (rads dT 20C) as it will supply this flowrate at 6M on CC3.

On setting 1 (in any mode), the boiler overheats and shuts down.

Can you find the pump curves for the other two pumps and post them.

P3:

UPS 25-55 180

Grundfos UP single-speed circulator pumps are designed for heating systems, while the three-speed UPS circulator pumps are used in central and district heating system while also being suitable for mixing loops in large systems. Both pumps provide reliable and maintenance-free operation.

product-selection.grundfos.com

P2:

UPS 15-50 130

Grundfos UP single-speed circulator pumps are designed for heating systems, while the three-speed UPS circulator pumps are used in central and district heating system while also being suitable for mixing loops in large systems. Both pumps provide reliable and maintenance-free operation.

product-selection.grundfos.com

I would suggest shutting the inlet/outlet isol valves on each pump and remove its head, give the pump ports a quick backflow from each side to prove the pump ports clear and push a tiewrap through the impeller vanes to prove clear.

I have already done that. There was no significant build up of debris etc.

I also checked the capacitor in P3, which was faulty. I have replaced that, but it made no discernable difference.

In desperation (the system failed before Christmas) I bought:
A Wilo Yonos Pico 25/1-8

https://wilo.com/gb/en/Products/en/products-expertise/wilo-yonos-pico/yonos-pico-25-1-8

I tried this in place of P3. It didn't make any functional difference.
I've tried it in place of P2. That hasn't helped either. It's currently still in place of P2.

I feel like there must be some restriction in the pipes somewhere, but I can't figure out how to identify that.

Also that UPS3 has a very disproportionate failure rate and unfortunately does not display the power in watts, a very useful aid on any A rated pump, most makes now do and also didplay the flowrate.

I do like these features on the Yonos Pico.

What is the output of the LPG boiler

42 kW

and its minimum output if it modulates?

I don't know how to find this out .
It does have a fast/slow flame that I can hear. Is this modulation?

and its ~ distance from the rads.

Do I need to measure the pipe runs (see above)?
If so, do you mean distance to the closest or furthest radiator? or an average distance?

Is the boiler heat only with no internal pump?

Yes - no internal pump.