How to run a home heating system efficiently

Iwannahurl

I recently got a heating controls upgrade, as approved by the SEAI.

The system is now divided into three independently controlled zones: upstairs heating, downstairs heating and hot water. It was in the usual 2-zone HW/HW-CH mode for ten years prior.

Unfortunately, since the upgrade the heating has undergone a personality change, and I am finding it difficult to make all the zones work efficiently and satisfactorily.

For example, even when the thermostat on the hot water cylinder indicates that there isn't a sufficient quantity of water at the selected temperature, the boiler still won't kick in unless its own thermostat is set high enough.

The result seems to be that the boiler is running even hotter, and more frequently, than before. That is not the desired outcome, surely?

Is there a 'theory' or a method for making all the parts of the system work to optimum efficiency, without the need for frequent adjustment and with confidence that it's saving energy?

shane0007

It sounds like it is not wired correctly.

Iwannahurl

That's my feeling, but is there any logical way to deduce that?

At the moment the return water temperature from the cylinder must be higher than the temperature set on the boiler, otherwise the boiler would kick in automatically.

How are the boiler and cylinder thermostats meant to relate to each other?

Previously I was advised by a boiler technician that the most efficient way to operate the boiler was "low and long", ie low temperature but over a longer time.

My plumber, after the "upgrade", is advising the exact opposite, ie set the boiler thermostat high and then both the hot water and the rads will get to the desired level (as set by the room and cylinder thermostats) much faster.

shane0007

Time set on timeclock for hot water demand gives power to cylinder stat. If stat is set to 60C but temperature is at 40C, this allows power to motorised valve. The motor turns in the valve which allows water to flow through it, but also hits a micro-switch which sends power to the boiler, telling the boiler to fire & switch on the circulating pump.

The boiler thermostat is only telling the boiler maintain a set flow temperature.

Once any of the components has been satisfied, i.e. the time control has passed or the cylinder temperature has been reached, the boiler switched live has been switched off.

Iderown

The set temperature for the thermostat on the boiler must be 5 to 10 degrees higher than the set temperature on your DHW cylinder thermostat. Otherwise you would be trying to, for example, heat something to 60C by using a heater at 55C.
Further, make sure that the DHW cylinder thermostat can sense the heated water temperature. If it is too low on the cylinder then it may be below (or too close to) the internal indirect heating coil. Many DHW cylinders now have a "solar coil" at the bottom. If that solar coil is unused then the bottom 1/4 maybe of your DHW cylinder will never get warm.

Iwannahurl

shane0007 wrote: »

Once any of the components has been satisfied, i.e. the time control has passed or the cylinder temperature has been reached, the boiler switched live has been switched off.

I have checked the cylinder thermostat and it triggers both the motorised valve and the circulating pump. However, the boiler doesn't necessarily switch on at the same time, which means that the boiler thermostat must be set fairly low.

Iderown wrote: »

The set temperature for the thermostat on the boiler must be 5 to 10 degrees higher than the set temperature on your DHW cylinder thermostat. Otherwise you would be trying to, for example, heat something to 60C by using a heater at 55C.

This is where my confusion (and dissatisfaction) arises. The cylinder thermostat, like the room thermostat, has actual numbers on it. I have it set at around 65 degrees. Unfortunately there are no numbers on the boiler (Firebird Super Q) thermostat, just a series of dots with Min/Max on either side. So there is no 'calibrated' relationship between the two thermostats.

The problem, in my perception anyway, is that the boiler and the rads seem to run much hotter now than before. Before the "upgrade" the central heating would be on at a moderate level (room thermostat around 20 degrees) and when in HW+CH mode a cylinder of hot water would just be there when needed. It's a large cylinder, needed to supply a pumped shower, and there was rarely an issue with lack of hot water.

Now the boiler seems to be working overtime to supply all three zones. Apart from the fact that it now seems to heat the rads to a much higher level than before, it also doesn't seem to be able to simultaneously provide enough hot water to the cylinder. I have taken to heating the hot water in the early hours of the morning, outside of times when the central heating is required.

I guess I must be doing something wrong, or misunderstanding how the new setup is supposed to work (after ten years of the old system). However, it is behaving quite differently and I'm not convinced that it is both energy efficient and operating smoothly. I want to reduce oil consumption, but not at the expense of having a heating system that is not functioning satisfactorily.

Iderown wrote: »

Further, make sure that the DHW cylinder thermostat can sense the heated water temperature. If it is too low on the cylinder then it may be below (or too close to) the internal indirect heating coil. Many DHW cylinders now have a "solar coil" at the bottom. If that solar coil is unused then the bottom 1/4 maybe of your DHW cylinder will never get warm.

The cylinder thermostat is about two-thirds of the way down. It has a rapid recovery coil (because of the pumped shower and the extra-large volume) but there is no solar coil. There is an electric heating element right at the bottom, but that has no effect presumably. We heat the water only with oil, and the electric option is only there as backup.

This prompts another question. To have a sufficient quantity of hot water in the cylinder at 60-70 degrees minimum, the water would need to be at this temperature at the level of the thermostat. Does that mean that the water at the top is potentially much hotter?

shane0007

The stat should not be powering the pump. It sounds more like an incorrectly wired issue. There is also no wired relationship between the room or cylinder stat & the boiler stat.

Ask the installer to return & test the system & to explain how the whole system works & interacts with the various components within it.

If you are still unhappy, you can request an audit from the SEAI as you received grant assistance from them. Decent installers will not have a problem with being audited.

Iwannahurl

I'm assuming that it triggers the pump (thought I heard a sound anyway).

Would it not need a pump so that the return water triggers the boiler thermostat, if its temperature is lower?

Apologies if these questions are far too Noddy-level, by the way!

shane0007

No apology required.
Are you mixing up terminology? Are you calling a motorised valve a pump?

Iwannahurl

No, the motorised valve is beside the cylinder.

I heard the pump, situated beside the boiler downstairs, or else believed I did because I assumed that the water needed to be circulated for the boiler to 'know' when to switch on. As Noddy might put it.

If not, how does the boiler detect that the water in the cylinder is at a lower temperature than the boiler thermostat?

shane0007

If the stat is wired to the pump, it is a serious wiring issue. It could potentially damage the boiler.

Don't go bald headed at the installer as I am not looking at the installation but something is amiss.

I previously drew this attached diagram of how a typical S plan heating system should be wired. It is fairly simple to follow. If it is not wired like this, then it is wired incorrectly, unless it is a gas boiler with volt free contacts. Then it should be wired as per the second attachment.

Iderown

Iwannahurl wrote: »

If not, how does the boiler detect that the water in the cylinder is at a lower temperature than the boiler thermostat?

In the setup here the boiler thermostat is in a port at the top of the boiler casing (along with an over-temperature cutout to protect against boiling if the first thermostat fails). It's sole purpose is to switch the burner off and on. It gets its supply from the OR connection of the microswitches in the motorised valves. It is enabled when there is a demand for heated water by any combination of the zones.

The DHW cylinder thermostat is electrically separate. It energises the motorised valve in the DHW cylinder water path.

Similar for the two space heating zones and their thermostats and motorised valves.

In some systems the circulation pump is activated along with the burner. In others there is yet another thermostat on the boiler for the circulation pump - pump over-run. (Ask if you need to know about this arrangement.)