bizarre coal burner system

[Neon Vagabond]

on a job doing a bathroom and the womans asked me to have a look at her heating system.
its a coal burner. ive never worked on one of these so im not sure how its supposed to work.
im very experienced with central heating systems in general though.

right so here it is.
main fuse supplies a pipe stat that feeds another pipe stat that feeds the motor/switch live.
its all seems very simple however. to get each pipe stat to make the link, it requires "turning down"
eg. setting them to 10degrees will turn them on, but setting to 90degrees will turn them off?
am i missing something here? anybody know how this is supposed to work?

 

[Darkwood]

Are they to prevent the water boiling thus possible pressure build-up ?

Is one a frost stat and the other a high temp stat or they both set the same?

 

[Neon Vagabond]

i imagine yes they are there to act as the boilers stat to regulate the water and stop it boiling like a big kettle. They both look the same. They are located under a kitchen worktop partially boxed in, not very good access, i have access to the junction box though

 

[Neon Vagabond]

why would there need to be a frost stat? if its in doors?

 

[Neon Vagabond]

yes they both look the same i meant to say earlier

 

[Darkwood]

why would there need to be a frost stat? if its in doors?

Sub zero temp's are not exclusive to outdoors although not the issue it used to be before well insulated houses came along, you provide little info so it was just a suggestion, without any kind of background to its age, the plumbing etc

 

[davesparks]

It sounds to me like a way of preventing a gravity hot water system from over heating

 

[Neon Vagabond]

im findinng it hard to explain the actual problem because i dont understand how the system works. I keep thinking about the pipe stats, ive never came across a stat that when you turn it up it clicks off.

the plot does thicken though, the woman says that the coal burner was replaced by a heating company within the last year, including around 13 re-visits to the job to try and sort it out.
The system has no zones. Hot water is only on when heating is on.
The pipe stats are located on 2 pipes next to pump/wiring centre
The immersor does not work because it is connected to a fuse box that is no longer connected to mains

Questions i'd like to know the answers to are;
1. What is the main purpose of the pipes that the stats are connected to? (flow? return? etc)
2. Why do these stats not work in the conventional manner?
3. What is the usual way of wiring a coal burning boiler?
4.Has anybody got a drawing?

 

[Darkwood]

Sounds like a poor design to start with for general functionality maybe your tasked to resolve a problem which comes down to poor design if it has never worked since been fitted.

 

[davesparks]

You will have to work out what the pipes are doing yourself.

I suspect they are working as a high limit to prevent overheating of something, probably the cylinder.
There will presumably be other controls in the system to control the pump?

 

[Neon Vagabond]

yes dave i think i understand what you mean, i definetly think that the intended design of this sytem is one which these pipe stats or at least one of them regulates the temperature of the water in the pipes much like the stats that are built into modern day combis etc.

There are however, no other controls in the system. No timer, no valves, no other stats
it definetly just goes:

mains>pipestat1>pipestat2>pump/switchwire

 

[Neon Vagabond]

what if i redesigned it?

Do you think it would work if i pulled out all the wiring ,started again by fitting new pipe stats to the flow/return pipes(both set at 60degrees).
and linking these into a 2 channel programmer/room stat/cyliner stat?, kinda like a conventional system without a valve?

 

[nunthe wiser]

I worked on something that sounds similiar, it was an old farm house where the Rayburn had been converted to burn heating oil. The cylinder stat controlled the pump as in a normal coal fired system and I had 2 stats which I was unsure of , a plumber I worked with repaired it and his explanation was that it was to stop cold water returning to the heat exchanger and causing rusting of said heat exchanger. 10 years ago so can't remember the details. Don't know if that's much help.

 

[Neon Vagabond]

I worked on something that sounds similiar, it was an old farm house where the Rayburn had been converted to burn heating oil. The cylinder stat controlled the pump as in a normal coal fired system and I had 2 stats which I was unsure of , a plumber I worked with repaired it and his explanation was that it was to stop cold water returning to the heat exchanger and causing rusting of said heat exchanger. 10 years ago so can't remember the details. Don't know if that's much help.

This helps me a bit because i suppose this is the intended purpose of the pipe stats, i'll now need to think about it a wee bit. thanks though

 

[Neon Vagabond]

right heres what im thinking so far.....

Say we set the pipe stat on the flow to 60degrees, its should want to heat that water to a minimum of 60 and turn off when it reaches temperature.
This water then flows up through the radiators and comes back on the return pipe.

Bare with me i'm still struggling..

Where does the water of the return pipe go to?
Does it just go back through the heat exchanger?

If it is a bad thing that cold water goes back to the heat exchanger then how does a stat prevent this from happeing?
theres no valve to stop it

 

[Leesparkykent]

right heres what im thinking so far.....

Say we set the pipe stat on the flow to 60degrees, its should want to heat that water to a minimum of 60 and turn off when it reaches temperature.
This water then flows up through the radiators and comes back on the return pipe.

Bare with me i'm still struggling..

Where does the water of the return pipe go to?
Does it just go back through the heat exchanger?

If it is a bad thing that cold water goes back to the heat exchanger then how does a stat prevent this from happeing?
theres no valve to stop it

A high limit thermostat should be fitted to the gravity flow pipe close to the boiler and set at 90°C. This should override any pump control, switching the pump on and dissipating any excess heat around the radiator circuit.
To prevent boiler corrosion due to condensation it is necessary to maintain the return water temperature above 45°C. This can be achieved by the use of a LOW LIMIT thermostat on the return pipe from the hot water cylinder, close to the boiler. The thermostat should make on temperature rise, preventing the circulating pump from operating until the gravity circuit is up to temperature.

 

[Neon Vagabond]

A high limit thermostat should be fitted to the gravity flow pipe close to the boiler and set at 90°C. This should override any pump control, switching the pump on and dissipating any excess heat around the radiator circuit.
To prevent boiler corrosion due to condensation it is necessary to maintain the return water temperature above 45°C. This can be achieved by the use of a LOW LIMIT thermostat on the return pipe from the hot water cylinder, close to the boiler. The thermostat should make on temperature rise, preventing the circulating pump from operating until the gravity circuit is up to temperature.

so do mean, the first stat allows the water to heat up to 90 then switched the pump on.
The water then flows through the heating system/hot water pipes and returns through a pipe that has another stat on it.
If the return water is below 45 degrees it turns pump off?

 

[solarsavings]

It's a mini max set up. The pump won't run at low temperature (below 50c) to protect the boiler from back end corrosion.

 

[Neon Vagabond]

e-energyinstaller.co.uk/wp-content/uploads/2015/06/boiler-stove-diagram.jpg

been having a look through some drawings via the magic of internet.
I think this looks like the system being described by some people on here but without a low limit stat on the gravity return?
Can anyone verify this?
Im probably not going to try and fix this womans heating system, ive agreed to wire her immersor back im still wanting to try and understand this system.

 

[Neon Vagabond]

sorry i meant to say " without a hi limit stat on the gravity flow" on that drawing