Heating System Puzzle

Why? If it works, why f..k with it?

If you insist, but be alerted that I have no intention if doing anything to the piping layout. There are five flats in the building, all converted at the same time, by the same contractor, in 1976. Nothing is known about there ever having been any scalding problems, and there are regular leaseholder meetings at which this would have been brought up. Even when the flat in question had a defective room 'stat, it was still perfectly habitable, just not properly responsive. Since the room 'stat was totally useless, and I have now fixed it, this is no longer an issue. I intend to set the thermostats as described above.

All of them.

Reply to
Davey
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mystery to me too. Folk here often recommend rejigging things to the latest formats when there's no evident need.

NT

Reply to
tabbypurr

The addition of a single zone valve could mean the HW temperature could be limited whilst the CH was running.

That is hardly the latest format and would cost all of one motorised valve.

I suppose we can't all be Luddites.

Reply to
Fredxxx

The OP has explained that it already is. Not by thermostat & valve, but by the relative heat throughputs & on times. Old school, but it works.

to solve a nonexistent problem

NT

Reply to
tabbypurr

Scalding was not my concern. There is always a kettle for the thickos to scald themselves if they want to.

I was thinking more along the lines of "let the DWH get as hot as the boiler stat and still allow the CH to work regardless of the HW stat". As it is not a nursing home or a home for special needs then the maximum HW temperature does not concern me.

Reply to
ARW

If you set the boiler stat at 130F (~54C) there's no danger of scalding hot water coming out of the taps.

But - unless the radiators have been grossly oversized - there *is* a danger that you'll shiver in cold weather. The flow temperature round the radiators probably needs to be around 80C (176F) to maintain a decent room temperature.

Reply to
Roger Mills

And that sums it up perfectly, to me. I appreciate all the input, but I have no intention of changing anything.

Reply to
Davey

My suggestion is

  1. Set the tank stat to the temperature you would normally use if this was a s or y plan
  2. Set the boiler stat to the maximim temperature that is safe if there was no tank stat
  3. Use the switch on the valve to give a live to the pump and boiler when the valve is operated.

This will allow the tank stat to control the HW temperature in the summer and stop the possibility of a lock out on the CH in the winter.

Reply to
ARW

snip

I have never used an 'S' or 'Y' plan system, so I will guess that the Tank 'stat. setpoint would be say about 130 F., and the Boiler 'stat about 140 F. ? That way, the boiler could always satisfy the tank heat requirement.

Ok. The pump needs to run whenever heat is required by the programmer and not prevented by the tank 'stat, due to the upside-down arrangement of the boiler and tank, so those connections need to remain.

To incorporate your mod. 3, and maintain the tank 'stat as a safety restriction on the over-generation of boiler heat, the output from the valve switch would need to be inserted between the programmer and the tank 'stat, or the output of the tank 'stat. But that would allow the boiler to run ONLY when the room 'stat is calling for heat, which is no good for DHW only.

So we leave the tank 'stat out of the HTG circuit, and let it just control the DHW temp. When the Room 'stat asks for heat, the valve opens, and power is fed to the switch from the Programmer HTG output, the same one that feeds the Room 'stat, or the Room 'stat's output feeding the valve motor, and when the valve proves open, sends power to the pump and boiler. This now controls the boiler temp. according to its own thermostat, and the Tank 'stat is taken out of the loop entirely, as in your condition 2, above. That should work, bearing in mind that the tank is now subject to whatever temp. the boiler is sending out, instead of its own thermostat.

[I use 'HTG' in preference to 'CH' because that is what the Programmer, and all my sketches, use].

I think it is unnecessary, but it is do-able without any pipework modifications, and all electrical components are already there. In fact, this modification requires only the moving of the wire currently going to a blank terminal on the Programmer to a terminal two spots away. Without digging into somebody else's airing cupboard, which would be a gross intrusion of privacy, I cannot know what the original intention and wiring were, and this might be the original design. Or not.

This I can do whenever I am next there, I see no reason not to. Thanks.

Reply to
Davey

That is correct. And had this been a gravity HW system that is what you would have had as there would be no tank stat.

I am not so sure that there is a need to rely on the tank stat if boiler stat fails closed. It may be worth seeing if you can get a manual for the boiler and see if it has an overheat stat built into it. I am sure my old Ideal Mexico boiler had one. Using the boiler stat to control the HW temperature in winter is something only you can decide on. If you decide that you need the tank stat as a safety feature then my mod is not doable (although you could always stick a pipe stat on the boiler flow pipe that would switch off the boiler and leave the pump running).

But let's keep it simple and cost free.

Sure the system is not going to be perfect but if it only takes a few minutes and costs nothing to do or undo a few tweaks then why not try it? My tweak would in winter just allow the rads to operate when the cylinder stat is satisfied and the room stat is calling and in summer allow the HW to be properly controlled by the cylinder stat.

BTW I found this a most interesting thread. Thanks for sharing it and for managing to work out your plumbing and wiring of a "B" plan. Everyone has learnt something.

Reply to
ARW

As I mentioned, I will do this last modification when I am next there, whenever that may be. Probably within a month, maybe less. I'll also look for a boiler manual, I have the model number somewhere. I think, from memory, it is an Ideal Standard, so should be easy to find.

It originally started as an appeal for help, but 'went all the way'.

Reply to
Davey

I haven't seen water temperatures in F for YEARS - I had to run a conversion.

AIUI you need to take the tank up to 60C (140F) at intervals to keep Legionnaire's disease at bay.

Andy

Reply to
Vir Campestris

Well, this system was installed in 1976, and as far as I know, all components, with the exception of the room thermostat (replaced by me last week), and the Zone Valve (replaced by an unknown 'Professional Installer' some months ago), are all original. Even the Room 'stat that I replaced was in deg. F., it was just past its 'Best Before' date.

An old-school engineer I worked with in the years around 1972-1977 called the abandoning of Imperial units 'Metrifuction'. He had a point......

Reply to
Davey

A different, but linked, puzzle. I was investigating the wiring of my house heating system yesterday, it is a proper 'C' System, thankfully. I was reminded that the wires from the cylinder 'stat, to terminal 8, and back from there to the valve motor, are not there, they are joined in the remote terminal box, and neither of them go downstairs to the main System J-Box. Functionally, it's not a problem, but for troubleshooting, it sucks. I noticed during a period of Hot Water use, with the Heating turned off, that terminal 10 remains powered, indicating either that the valve is stuck Open (possible, it was once before), or that the tank 'stat is remaining closed. It was the boiler 'stat that was controlling the boiler operation.

Before I open up the access to the tank 'stat, (a fairly large upheaval of the bathroom), what are optimal operating setpoints, or at least their relationship, for a 'C' System? I seem to remember that the cylinder 'stat is already set low. I know that one test for the valve is to shut off both Heating and Hot Water and see if the boiler will still run, and that shows if the valve is stuck in the Open position, that is how the original failure was detected.

Any help welcome. The system works, but like the one in the flat, the 'B' System, it can be made to operate better.

Reply to
Davey

When you say that the heating was turned off, was the HW also turned off? If not, it's behaving like it's supposed to. If you're using hot water, and reducing the tank temperature below the stat setting, then - providing there's a HW demand from the programmer - you'd expect the boiler to run to heat the tank up again.If there's *no* Hw demand, the tank stat will have no effect even if stuck closed. If the boiler runs under those circumstances - without the pump also running - it must be being fed from the valve's NO contact, implying either that the valve is stuck open (if the tank actually gets hot) or just that the valve's switch is stuck in the position it would only normally be in when the valve is open, even though the valve is closed. Under these circumstances, the boiler would cycle on its own stat without actually heating the tank.

With regards to stat settings - when everything is working properly - I would set the tank stat to 55-60 (depending on how hot you like your hot water) and the boiler stat to about 80 - assuming it's not a condensing boiler. [Unlikely with a C-Plan system]. That will give the CH a decent flow temperature, and also give the thermo-syphon HW system enough urge to prevent it taking all day to heat the water.

Reply to
Roger Mills

No, the HW was still on.

SWMBO stated that there was plenty of hot water for an extended shower, and I have never found it lacking, so the tank is being heated ok. If anything, the hot water is too hot, but not scalding. When I had a problem before, the valve was stuck in the open position, but it freed up ok. It might have done the same thing now. The only way we knew there was a problem at all was when the boiler service guy turned off the programmer outputs, but the boiler still ran according to its own thermostat, which it should not have done.

Correct, it's an older boiler, and the service guy recommends that I stick with it as long as it runs. I just had it 'de-kettled', the system flushed, and new inhibitor added.

Thanks, that makes sense, and sounds similar to what I think is there now.

Reply to
Davey

The fact that plenty of hot water was coming out of the top of the tank doesn't necessarily mean that the tank stat is above its set point and therefore not calling for heat.

As hot water is drawn off from the top, it's replaced by cold water at the bottom. There will be a vertical temperature gradient within the tank. Depending on at what height the stat is fitted, it may well trip and turn the boiler on even though the water at the top is still piping hot.

My belief is that your system is doing exactly what it says on the tin!

Reply to
Roger Mills

Well that's good news! When I get the opportunity, I'll get access to the tank, and operate the 'stat, while checking the operation. Access to the valve is very difficult (of course, it seems to be normal), but the J-Box is a bit easier. This is not, however, a priority, as the system indeed produces hot water and heating.

Reply to
Davey

Davey posted

How did you do that? Limescale remover?

Reply to
Big Les Wade

A local well-regarded plumber came round with a pressurising pump and container, and circulated some cleaning solution. He also removed and cleaned the expansion tank, replaced the grotty fill valve, and put inhibitor into the system. Now it's nice and quiet.

Reply to
Davey

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