Inherited a seemingly ancient CH system...

Not sure if this gives any indication of how the system is wired, but this morning, while checking the cylinder stat temperature during a timer on period (pump running) I turned the cylinder stat down to below 45 degrees C, and the pump immediately stopped. As soon as i turned it back up to above 60, it started again.

BTW, should the cylinder stat be covered by the insulating jacket, or left open to the air?
 
The cylinder stat is low power and can be covered or not. But no need to cover it.

But the immersion heater connection box should never be covered by insulation.

As I predicted your cyl stat is correctly connected to turn off the boiler and pump when the cyl has reached the set temperature.

But the deficiency in that very simple system is that when the heating is on the cylinder is always on. Potentially heating the cylinder up to a higher than the recommended maximum of 60 C. Wasting energy and giving a risk of scalding. Quite apart from the inconvenience of fluctuating hot water temps.

Tony
 
Agile said:
The cylinder stat is low power and can be covered or not. But no need to cover it.

But the immersion heater connection box should never be covered by insulation.

As I predicted your cyl stat is correctly connected to turn off the boiler and pump when the cyl has reached the set temperature.

But the deficiency in that very simple system is that when the heating is on the cylinder is always on. Potentially heating the cylinder up to a higher than the recommended maximum of 60 C. Wasting energy and giving a risk of scalding. Quite apart from the inconvenience of fluctuating hot water temps.

Tony
Click to expand...

I see, thanks. Currently cylinder stat is covered but the immersion heater is wired only to a switch on the wall in the airing cupboard, which is uncovered.

Presumably at the moment then, as the room thermostat is at minimum, the pump is running because the cylinder stat is telling it to (hence it stopped when I turned down the stat). But that being the case, why would the pump continue to run when the boiler is not lit? If the cylinder stat is requesting heat, shouldn't the boiler and pump run together until 60 is achieved, at which point the both shut off?
 
The pump will run but the boiler will turn off when its flow temperature reaches the set value.

It should be set at least 10 C above the cyl stat setting.

Your older boiler does not modulate so it just turns off when it reaches the set temperature.

Your old cylinder only has a smallish heating coil and that is unable to absorb all of the boiler's power output.

Tony
 
Ok... So the boiler is shutting off because the water going through it has reached the temp on its own stat (whatever number 5 equates to as it stands). But the pump is still running to pump the water in the pipes/coil (which is hopefully hotter than that in the cylinder itself) around the system to heat the cylinder water to whatever the cylinder stat requests....?
 
Correct.

There is a problem though. In the winter the pump and boiler will need to be operating in order to heat the radiators. However, your installation (i.e. without a motorised valve for the hot water cylinder) means that water from the boiler will also be being circulated through the hot water cylinder. So even when the cylinder thermostat switches off, it won't be doing anything because the central heating will keep the boiler and pump running and will continue to circulate water from the boiler around the hot water cylinder.
 
stem said:
Correct.

There is a problem though. In the winter the pump and boiler will need to be operating in order to heat the radiators. However, your installation (i.e. without a motorised valve for the hot water cylinder) means that water from the boiler will also be being circulated through the hot water cylinder. So even when the cylinder thermostat switches off, it won't be doing anything because the central heating will keep the boiler and pump running and will continue to circulate water from the boiler around the hot water cylinder.
Click to expand...

Right, which leads to the problem Tony details where the cylinder heats up further, regardless of the cylinder stat temp? Again, presumably that problem is solved with a second motorised valve, then?

I wonder how the previous home owners managed around this problem??
 
Indeed that's exactly what happens.

There are still lots of systems around without any thermostatic control of the hot water at all and the boiler stays 'on' whenever the timeswitch is 'on'. Most are old solid fuel systems that have been converted to run on other fuels. At least yours is halfway there, you have a pumped supply to the cylinder and thermostatic control of the hot water during the summer.

Systems like yours were still being installed in the 1980's.

It wouldn't appear to be a major job to install a second motorised valve
 
True. I did notice when we initially moved in that the previous owners had left the immersion heater switched on. Is it possible they just used the immersion heater for the hot water all the time, and the boiler only for the CH? Not sure how they would have stopped the water circulating through the cylinder, though. Anyway, suppose that's not my mystery to solve.

On to find a plumber, then..!
 
greenstarthree01 said:
Not sure how they would have stopped the water circulating through the cylinder, though.
Click to expand...

Closing the red valve in the pipe below the motorised valve would stop the water flowing through the cylinder. I wouldn't recommend it though because when the hot water is switched 'on' the pump and boiler will be running, but with the red valve closed and the heating off (motorised valve closed) as there isn't a bypass, there won't be anywhere for the water to go.

In the winter, if the motorised valve is wired up to control the pump and boiler when just the heating is 'on' then they may have left the hot water 'off' as the boiler and pump would only run when the heating motorised valve is open. The danger is someone inadvertently switches the hot water 'on' when the valve is closed.
 
Last edited:
Thanks stem, and everyone. Apologies again for the basic questions, I can feel the head shaking from here! :D Hopefully it might help someone else, though!

Will update with any work that goes on. Anyone working in Yorkshire, let me know :LOL:
 
I also have inherited an old system: One pipe, Ideal Mexico. Prior owners had a BG cover so knowing how cheap it is i have continued with it. If you renewed it they would maybe have fixed it. Last service they did recently guy said it in top shape. To replace with 2 pipe would mean moving boiler to the loft as it couldn't be where it is for regs. (One floor place) Because of work involved, said it would be expensive: £10k (!) Boiler/scaffolding required/two pipes (plastic though i have one copper already) Haven't heard back after 4 months now! Am going to attempt to it 2 extra rads where there should be heat and will post for advice. Lot of people say these systems are fine. Mine heats up quickly and is v hot. By the time you get your money back if you update it the new boiler would probably need replacing....However your system does sound older.
 
chestercity said:
I also have inherited an old system: One pipe, Ideal Mexico. Prior owners had a BG cover so knowing how cheap it is i have continued with it. If you renewed it they would maybe have fixed it. Last service they did recently guy said it in top shape. To replace with 2 pipe would mean moving boiler to the loft as it couldn't be where it is for regs. (One floor place) Because of work involved, said it would be expensive: £10k (!) Boiler/scaffolding required/two pipes (plastic though i have one copper already) Haven't heard back after 4 months now! Am going to attempt to it 2 extra rads where there should be heat and will post for advice. Lot of people say these systems are fine. Mine heats up quickly and is v hot. By the time you get your money back if you update it the new boiler would probably need replacing....However your system does sound older.
Click to expand...
fooking £10k your pulling my plonker right :cautious: , where do you live ill do it for 9k :ROFLMAO:
 
You must log in or register to reply here.
Back
Top