Why won't my old Rayburn heat water when pumped?

[montyjohn]

I'm trying to understand why I can't heat my radiators with the Rayburn.
My last house had a combi boiler so this is all new to me.

The Rayburn is a oil wick burner. 33" wide Royal with circa 1" pipes coming in/out of it. The unit itself gets up to temperature well. Burner glowing red when on full blast.

It will heat up the cylinder with gravity circulation just fine. Gets the water very hot.
As soon as I turned the pump on that serves the radiators, the radiators all warm for a bit, then everything goes cold.

I assumed that the pump was upsetting the gravity loop as the pipes going in an out of the Rayburn were also now cold.
Here is how the system worked?



So with my infinite wisdom, assuming the gravity loop and pump aren't playing nicely, I converted it to a sort of pumped S plan using a couple of gate vales (with no control on the Radiator loop).

So I now have this:



Gate Vale 1, I leave just 10% open. This is a safety thing should the pump fail. I've checked that it will still heat the tank in this position and it does.
With G1 fully open, pump off and G2 closed, it behaves exactly as it did before, the cylinder heats up well. So I've not broken anything which is good.

As a test I closed G1, and left G2 at 50%, and after an hour or so, everything is luke warm to cold. Even the pipes going down to the Rayburn. How can this be?

I believe the pump is working well because with G2 fully open and G1 at say 10%, there's enough pressure difference to over pump back into the header tank. Keeping G2 at 50% seems to solve this.

But still no real heat.

Does a Rayburn produce so little heat that it can't heat my radiators (5 of)?

All bled, plus I have had heat in them for 10 minutes or so when using the original setup.

Maybe the pump is too powerful and water doesn't have time to heat in the Rayburn, but this seems to break the rules of thermodynamics.

Only other clue is when I drained the system down, and filled it back up again, radiators didn't need bleeding at all. This surprised me.

What am I missing here? Any clues?

Many thanks

 

[Stevers]

Are the radiators in series or parallel - if in parallel are you able to heat all of them (top to bottom) one at a time?

I can't help feeling that one of those mysterious 'air locks' could produce symptoms like you're seeing.

 

[montyjohn]

Are the radiators in series or parallel - if in parallel are you able to heat all of them (top to bottom) one at a time?

I can't help feeling that one of those mysterious 'air locks' could produce symptoms like you're seeing.

I have no idea what configuration the radiators are in. I think parallel.
I've just turned off all radiators except for one, and the one after about half an hour has got pretty hot.
This is with the pump running.

The the system clearly can heat one radiator very well.

I miss-counted earlier, it's six radiators not five.
But will all on, as a guess they seem to max out at 30 degrees.

Maybe this is just normal for an old oil Rayburn, and what I need is a much more powerful combi oil boiler.

 

[fernicarry]

Does a Rayburn produce so little heat that it can't heat my radiators (5 of)?

That's entirely possible. Has it even heated the radiators? What sort of weekly oil consumption does it get through? If you know that you could work out the calorific value of the heat input and come up with a rough number of kWh's although if its a vaporising burner it won't be especially efficient so you'll need to discount that number.

For comparison our oil fired Aga only puts 1 or 2kW into the water boiler which is plenty to keep a hot water cylinder scalding hot but wouldn't go very far with space heating demands. It goes through about 50l a week iirc.

 

[Cubist]

To my mind theres something very wrong with both these diagrams. I had always understood that a 'single' loop was used with these older systems that routes hot water through, first of all, the hot water cylinders coil and then onward to the radiators before returning to the stoves water jacket,

What direction is the pump moving the water? Also, those gate valves would appear to be capable of entirely reversing the primary direction of hot water flow and G1 could induce a burst of the Hot Water cylinder and or the stoves water jacket by blocking the pipe usually used for expansion from both.

 

[Cubist]

Another of my afterthoughts - presuming that a thermostatic switch located on the pipe from the stove hot water jacket is used to switch on the pump, how long did you wait before checking how warm the radiators became and did you check first to see if the hot water cylinder had already reached its optimum temperature?

 

[montyjohn]

To my mind theres something very wrong with both these diagrams. I had always understood that a 'single' loop was used with these older systems that routes hot water through, first of all, the hot water cylinders coil and then onward to the radiators before returning to the stoves water jacket,

The problem with running the tank and radiators as a single loop is you lose the ability to heat just one or the other. Inless you have bypasses with valves on them, which in effect is what I now have with the S-Plan layout.

If I was keeping the system long term I would use actuated valves normally open instead of gates vales to give full control over the temperatures.

What direction is the pump moving the water? Also, those gate valves would appear to be capable of entirely reversing the primary direction of hot water flow and G1 could induce a burst of the Hot Water cylinder and or the stoves water jacket by blocking the pipe usually used for expansion from both.

Pumped away from the Rayburn (hot side).
Yes closing both valves off wouldn't be a good idea. This is why I have the pump bypass valve that I'll leave 10% open.
Again, if this were to be a long term solution I could use a normally open valve here instead, or perhaps just a check valve.
I just needed a cheap quick way to test what the system was capable of.

presuming that a thermostatic switch located on the pipe from the stove hot water jacket is used to switch on the pump, how long did you wait before checking how warm the radiators became and did you check first to see if the hot water cylinder had already reached its optimum temperature?

The only thermostat is the palm of my hand.
It's been running for about four hours now.
Radiators are about 30 degrees.
Tank is a little hotter, I would guess about 40 degrees. Only way to get the tank hotter is to open G1, close G2 and switch the pump off.

 

[a twig]

According to the internet the old Rayburn royals kick out between 8 or 9kW so about a third of the output of a modern combi.

Just going off rule of thumb you’d typically want 1.5kW per rad (ignoring sizing / flow rates etc) so you shouldn’t be too far off if a little underpowered.

If that pipe layout is correct, I’m not sure your valve arrangement in your second diagram is ideal. G1 and G2 are just doing the same thing aren’t they? As in they both allow hot water back towards the hot water tank, just one is before the pump and one is after?

Might well be reading it wrong so happy to be corrected but you could test my theory by leaving G1 at 10% and closing G2 with the pump on which should force the hot water from the Rayburn round the rads and they should get hot while the temp in the HW tank cools

 

[a twig]

An S plan normally has the pump on the outlet of the heat source (Rayburn in this case) then a 3 way valve to go to HW or CH doesn’t it? Like this:



EDIT:

When you ran pump with the system in its original configuration how long did you leave it running?

Our old wood burner ran two rads off a back boiler on a dedicated circuit and when we turned the pump on we got the same scenario - effectively until the whole system warmed up you could think of the circuit as “water cooling” the back of the wood burner for the first 45 minutes or so until all the cold water that had been sitting in the rads had done a few laps and warmed up properly

 

[Cubist]

So, in effect, you've tried to convert a single loop system to a a dual that allows selection between hearing and hot water. When selecting the gate valves did you ensure that they did not restrict the normal flow rate below the level of the 22mm pipes? Given that yours appears to be an older system I think a 'parallel' service is unlikely and your radiators are more likely plumbed in a single circuit. This may explain the relative 10 degree heat loss particularly if the coolest rad is the furthest away from the stoves heat jacket. What type of radiators are currently installed, pressed steel panel types or something more substantial?

 

[montyjohn]

An S plan normally has the pump on the outlet of the heat source (Rayburn in this case) then a 3 way valve to go to HW or CH doesn’t it? Like this:

View attachment 18451

EDIT:

When you ran pump with the system in its original configuration how long did you leave it running?

Our old wood burner ran two rads off a back boiler on a dedicated circuit and when we turned the pump on we got the same scenario - effectively until the whole system warmed up you could think of the circuit as “water cooling” the back of the wood burner for the first 45 minutes or so until all the cold water that had been sitting in the rads had done a few laps and warmed up properly

The plan you showed is effectively what I have.
Except I don't have one of the valves on the radiator side so it's always open and I added a bypass that I can crank open 10% for safety reasons. Not needed with a modern boiler, but critical for something like an old Rayburn.

I could modify your diagram to match my system as follows:





I've read quite a few different kw ratings for an old Rayburn such I'm not sure what to believe.
If the 8kw one is correct, I suspect most of that is emitted directly by the Rayburn itself. Say 5kw to the room it's in, leaving only 3kw for radiators and hot water. So two radiators would be max which to be fair, isn't far off what I'm finding.

 

[montyjohn]

So, in effect, you've tried to convert a single loop system to a a dual that allows selection between hearing and hot water. When selecting the gate valves did you ensure that they did not restrict the normal flow rate below the level of the 22mm pipes? Given that yours appears to be an older system I think a 'parallel' service is unlikely and your radiators are more likely plumbed in a single circuit. This may explain the relative 10 degree heat loss particularly if the coolest rad is the furthest away from the stoves heat jacket. What type of radiators are currently installed, pressed steel panel types or something more substantial?

Whilst the Rayburn and the pipework from it all look mid century, the cylinder and header tank are dates 2023.
The radiators look like the cheap panel radiators that you would buy 20 years ago also.
So I think the plumbing for the radiators is all quite new, but may be a DIY job, so could be any layout.

Gates are just cheap gates 22mm gates, so do restrict a bit. But with gravity only, still working very well, and with the pump on level 2, and the gate fully open, it overpumps so the gates don't appear to be causing a restriction.

 

[a twig]

So what happens if you leave G1 at 10% and close G2 then - does the radiator heating improve?

Or just close G2 to 10% if you don’t want it fully closed

 

[montyjohn]

So what happens if you leave G1 at 10% and close G2 then - does the radiator heating improve?

Or just close G2 to 10% if you don’t want it fully closed

Radiators max out at about 30 degrees. Bun running for a few hours now.
The rooms are about 18 degrees to be fair so not a problem right now, but it's mild right outside.

If it's down to a heat capacity issue with the Rayburn (which I think it is) then I'll look into installing a much beefier condensing oil boiler.

 

[paulc]

According to the internet the old Rayburn royals kick out between 8 or 9kW so about a third of the output of a modern combi.

Just going off rule of thumb you’d typically want 1.5kW per rad (ignoring sizing / flow rates etc) so you shouldn’t be too far off if a little underpowered.

I've got a total of eight radiators plus a plinth heater powered by a (nominal) 32kW gas combi boiler. Because I have nothing better to do, also have a heat meter in the system to monitor exactly how much energy is being generated & used. At start up, it might peak at 8-9kW before dropping down to ~4kW and average 5-6kWh. It has taken a little while to get the system running effectively, and the two things that helped enormously was to balance the radiators and turn the pump speed right down.

@montyjohn - Try turning your pump speed down as low as it will go. It is possible that you are pumping water round too fast and it doesn't have enough time to pick up heat from the boiler. If the Rayburn will produce 8-9kW, that should be plenty for just six radiators (unless they are all huge beasts).

 

[Cubist]

I'm trying to understand why I can't heat my radiators with the Rayburn.
My last house had a combi boiler so this is all new to me.

The Rayburn is a oil wick burner. 33" wide Royal with circa 1" pipes coming in/out of it. The unit itself gets up to temperature well. Burner glowing red when on full blast.

It will heat up the cylinder with gravity circulation just fine. Gets the water very hot.
As soon as I turned the pump on that serves the radiators, the radiators all warm for a bit, then everything goes cold.

I assumed that the pump was upsetting the gravity loop as the pipes going in an out of the Rayburn were also now cold.
Here is how the system worked?

View attachment 18443

So with my infinite wisdom, assuming the gravity loop and pump aren't playing nicely, I converted it to a sort of pumped S plan using a couple of gate vales (with no control on the Radiator loop).

So I now have this:

View attachment 18444

Gate Vale 1, I leave just 10% open. This is a safety thing should the pump fail. I've checked that it will still heat the tank in this position and it does.
With G1 fully open, pump off and G2 closed, it behaves exactly as it did before, the cylinder heats up well. So I've not broken anything which is good.

As a test I closed G1, and left G2 at 50%, and after an hour or so, everything is luke warm to cold. Even the pipes going down to the Rayburn. How can this be?

I believe the pump is working well because with G2 fully open and G1 at say 10%, there's enough pressure difference to over pump back into the header tank. Keeping G2 at 50% seems to solve this.

But still no real heat.

Does a Rayburn produce so little heat that it can't heat my radiators (5 of)?

All bled, plus I have had heat in them for 10 minutes or so when using the original setup.

Maybe the pump is too powerful and water doesn't have time to heat in the Rayburn, but this seems to break the rules of thermodynamics.

Only other clue is when I drained the system down, and filled it back up again, radiators didn't need bleeding at all. This surprised me.

What am I missing here? Any clues?

Many thanks

I have kept coming back to the diagrams above because I haven't been able to quite put my finger on why they have piqued that annoying itch that says I'm missing something. On this latest visit I think that original itch was created by my paying too much attention to the second diagram than I did the first, albeit that I had already seen part of the irritant that triggered my disquiet and that I had been thinking of the diagrams as depictions of the physical layout of the pipework rather than, as I should, a logical model. Reflecting more carefully on the 'Original Set Up' diagram I now believe that it must be incorrect. The siting of the CH Pump in that model implies that the Hot Water Cylinder would either never get hot or it would take a month of Sundays to do so. To explain; when that Pump is powered up it will create positive pressure toward the Radiator circuit and momentarily reduced pressure in the Rayburn's water jacket thus creating the initial circulation current in the pipes which would then be maintained by the continued operation of the pump. In other words; the cooled water from the radiators would be drawn back toward the Rayburn where it would be heated again and recirculated.

Clearly this CH and Hot Water System must have worked in the past but the only way it could have done so at all efficiently for both the Hot Water Cylinder and the Radiators would be if the Pump was situated in a single pipe from the Rayburn that then fed both either simultaneously or in series. In a serial CH system either the HW Cylinder or the Radiators would be given priority for the hot water directly from the stove before passing that same water on to either the Radiators or the HW Cylinder. Whilst some delay in the warming of some components of the system may be observed this would largely be off-set by the speed with which the water circulates within the serial circuit. A simple 'un-managed' dual circuit system can also be implemented to use a single pump, which would appear to be the case in @montyjohn s home, with the pipe layout he depicts above.

But then, if the first diagram is wrong then so too is the second, and what are the implications on the operation of the Gate (G1 and G2) Valves introduced in that model?

As @montyjohn reports; setting G1 fully open and G2 fully closed produces exactly the Null result it should insofar that, effectively, the GV settings replicate the original pipe layout in the first diagram.

However, when G1 is fully closed and G2 is 50% open then one might expect the result to be that the Radiators reach their optimum operating temperature fairly rapidly whilst the HW Cylinder takes longer to reach its. But this seems not to be the case insofar that, as @montyjohn states, everything, including the pipes back to the Rayburn, were lukewarm to warm at best. I'm aware that constricting a pipe can produce huge impacts on flow rate, velocity and induce pressure losses. Sadly understanding all these effects to then formulate an explanation is beyond my schoolboy physics - at present - but these must be operating to produce the observed results - unless of course the Rayburn was not operating, which might explain why the primary output pipe from it was also cold/lukewarm if indeed it was.

At the moment I'm assuming that the later alterations to the gate valve settings were aimed at getting some of the Rayburn's heat distributed to the Radiators and the Cylinder without creating a fountain in the loft but I'm now fairly sure that the root of these problems lies in the impacts on flow rate, velocity and pressure loss rather than anything dramatically wrong with either the Rayburn's performance or the original pipework layout.