filling up a Back Boiler system

[TerryWaite]

I am due to go and replace a pump on a back boiler system tomorrow, all the rads are cold, when coal fire is on, rads are full, cold feed not blocked, the pump is spinning but not very strongly at all, you can stop it rotating with the tiniest bit of pressure from a screwdriver, and it looks donkeys years old.

I am going to change the pump, that is the diagnosis I have come up with, however, never worked on a back boiler before, I dont even know what one looks like! im hoping I dont have to touch any of that, just drain down, change pump, fill up?? Somebody told me backboiler systems are bad for air locking, is this true?

 

[cdodds2004]

not really anyworse than any other open vented system, but can be a pain! can you not just isolate the pump via pump valves and swop out?

 

[dancinplumba]

usually they are open vented, this makes em prone to airlocks can you not isolate pump ?
imo

 

[dancinplumba]

too fast for me mr dodds lol

 

[cdodds2004]

LOL like a whippet tonight! but you can see a trend in the correct response trail of thought is the same!

 

[hammers4spanner]

Depending what state the pump is in as to wether i drain or not sometimes its worth draining just in case it has potential to go pear shaped.

 

[Roger Welton]

My experience with back boilers is that the water condition tends to be very poor, and benefit from a good old flush.

 

[dancinplumba]

you could cap off feed an vent, helps create a vacumn ?

 

[tamz]

Are the people new to the house?
A coal fired boiler needs to have a good fire going before you get much heat. A small fire will only give luke warm rads.
If it is an open fire the output is only around 18000 - 25,000 btu at full pelt (depending on the model). Room heaters (glass fronted Parkrays , Rayburns etc) give out around 40 - 50,000 btu, but again only at full blast.
There is usually no need to drain them. Check it is not a primatic. The existing pump may be a 180 if it is old so you may need a 30mm adaptor if there is no movement on the pipes.
Some old pumps like SMC's (blue ones) work different and are easily stopped.
Apart from that if you are draining it, it is no different to any other open system except make sure the fire is out.
You will be there for an hour or so after you refill it waiting on it to heat up to check it. Don't be tempted to turn the pump on before the fire is up to temp or you will be there all day.

 

[bennygas]

if the system's in a bit of a state, there's a good chance the pump valves might not close/seal fully. make sure you got plenty of rags if you aren't planning on draining. where's the pump? it'd be lovely if it's under a downstairs suspended floor (without wires and junction boxes littering the undersite of course!). got a mate with a pipe freezer? could save hassle with filling back up and getting it to circulate, it might even pay to change the pump valves if they're u/s. count your blessings - sounds like it aint got a primatic cylinder. just noted your mention of coal fire - not my field. tamz advice seems good.

 

[SimonJohns]

I recommend a pipe freezer. You may have too many issues with air locks. And valves seizing. For £45 from your local hire shop all these issues can be avoided. And job done in half the time.

I'm talking about an electric freezer and not a can of co2

 

[bennygas]

i still got my old freezemaster in me garage. great machine. one of the freezeheads stopped working though - think much have refrigerant leak or something.

 

[Leo21]

Could this be a blocked return pipe into the bbu?

 

[TerryWaite]

Hi All, many thanks for all your advice

I went round today and managed to isolate the pump on the valves, swapped it over, put the fire back on to warm up for a bit and then started the pump but got virtually nothing through. The pump was running fine, I felt the pipe on the inlet side of the pump, and it got barely warm for a bit, but then just went cool again.

The fire the guy has is a glass fronted coal burning thing, not sure of what you would call it exactly, not worked on many of these types of fires or BBU's for that matter before, I have posted some pics below but the quality isnt the best on my cameraphone sorry.

One thing to note is, I know this is a crazy way of testing and will make you laugh, but the coals didnt seem to be giving off all that much heat. I could put my hand physically in the fire (above the flames obviously) for atleast 20 seconds or so before my hand started getting really hot. Now if it cant burn my hand, how the hell can it heat up 6 rads?.

I left the job and told the customer I would be back at a later date, luckily, I know the guy and he knows I am a bit unfamiliar with back boilers, but nonetheless I would like to get to the bottom of this!

I have included a diagram and pictures of the cylinder cupboard, which is on the ground floor, a couple of metres away from the fire.

Tamz said something about checking it is not a primatic cylinder. Again, whats one of these! this cylinder has a coil going to it (im sure its a coil) but there are no 2-port or 3-port valves controlling it, no fancy timers or programmers, just a pump and an immersion heater.

Is the immersion heater just for backup in this system here? And how do I know if it is a primatic cylinder or not?

What u guys think the problem could be? Blockage-need powerflushing, or air lock? Or fire not generating enough heat?

I rang guy a few hours later and he said the rads were just barely warm.

Another thing of note is, there are no drain offs anywhere! How would you drain this system? Or are you able to drain BBU's when you take the fire out?
View attachment 6206View attachment 6205View attachment 6209View attachment 6208View attachment 6207

Many Thanks

 

[Leo21]

Does it manage the hw with just the fire? This would prove if there's enough heat.

 

[tamz]

I can't see your photos Terry.
It is a room heater that is fitted.
Basic system design, gravity hot water with 1" revolves, pumped heating usually controlled by a spur switch on the wall and it should have a high limit pipe stat and sometimes a low limit too. The immersion is for hw in the summer if they don't want to light the fire.
If it is a primatic cylinder the flow and return will go straight into the cylinder with no tees for feed or expansion and no F&E tank.
Room heaters have an output of around 40 to 50 000btu depending on the model but only if they are burning anthracite, coalite or something similar. Burning logs will never create enough heat to heat the rads as the boiler will cool as fast as it heats although it will heat the hw if the pump is off. The manu's state they will heat 8 rads or 10 rads etc but that is not heat like you know it from a gas or oil fired system.
The reason i asked if they are new to the property is if they have had it for years they would know how to work it and its limitations.
If you could hold your hand in the fire it is not generating anywhere enough heat to do the rads. Even burning the correct fuel with a good fire going the rads will never get really hot like with gas or oil and if they do it is only for a short time. The rads need to be checked back quite severely to get them to work half decent. Start balancing them with the ls valves open only 1/4 turn and go from there. Too much water flow through the rads will kill all the heat from the boiler and affect the hw too. We used to install them with 6mm pipe in the 70's for that reason. They don't need much flow.
Check the thermostat is working ok as it may be stuck shut and open the damper fully.

Have a read through this to get an idea how they operate
[DLMURL]http://www.parkray.co.uk/assets/downloads/Con-Cap-Che-cla-Userguide.pdf[/DLMURL]

 

[TerryWaite]

 

[TerryWaite]

Been back again, dont think it is a primatic cylinder. Just an ordinary one. The tenant is new to the property yes but there is literally no heat going anywhere, it is pathetic. I dont know the make and model of the fire, and dont want to mess about with it trying to pull it out or anything, but I have posted pics if you can see these.

The guy is burning anthracite smokeless coal, but there really doesnt seem to be much heat coming from the fire at all. The fire wasnt burning strong when these pics were taken, but the guy said he has had loads of coal on it for hours and hours and still nothing.

How does the BBU work, I can see the smoke going up the flue but cannot see up the flue very far. There was a big plate just beneath the flue opening which I presume is some sort of damper? There is also a catch on the top of the fire at the front but was very hard to operate. I think the property has been empty for some time but I do not know how long.

I might be a bit out of my depth on this one having not done much on BBUs, but have paid for a new pump so cannot really charge for this if the system still isnt working! The fire just doesnt seem to be getting hot enough, is there any way of opening any dampers/ openings which I have missed? Thanks Tamz for your advice so far really appreciate it! And everybody elses advice too.

 

[TerryWaite]

Also included a diagram of system here

 

[tamz]

That is one seriously neglected roomheater. It is a Parkray 88GT mark 1 btw. Been in since the 70's. It is in really bad condition and has a few parts missing. By the looks of the "fire" that is set, it will never heat anything. There is too much wrong with it to even tell you where to start and it need the attention of someone who knows what they are doing. It may be salvageable but at what cost is hard to say without seeing it.
I think you may have to pass this one on. I'd still charge him for the pump.

 

[TerryWaite]

Thank you very much mate, think that is exactly what I will do, could spend forever fannying about with that thing to no avail. It has had its day by the sounds of it.

 

[tamz]

Not worth the hassle Terry.

 

[ambrosia]

Thank you very much mate, think that is exactly what I will do, could spend forever fannying about with that thing to no avail. It has had its day by the sounds of it.

dam I was reading with interest, I was almost jealous that heating system makes a change from the strict diet of endless combi boilers i'm on, I wanted to find out how you were going to fix it

No happy ending for this post/thread