Help connecting wireless thermostat to boiler

Makes much sense thank you.

With older non condensing boilers you also had to guard against running it too low since you might reach a return temperature where the boiler would start to condense water out of the flue gasses. Since the boiler was not designed to deal with this (and probably had an upward firing flame under the main heat exchanger), this would dump slightly acidic water all over the (probably steel) heat exchanger and boiler metalwork, causing accelerated corrosion.

Modern boilers like yours are designed to induce condensing of the gases (and the water is collected and dumped to a drain without ruining the boiler). Forcing the phase change from the gas state to liquid recovers the latent heat of vaporisation that is in effect stored in the flue gas.

In effect you were manually doing weather compensation...

Modern systems that have it normally have an external temperature sensor, and use a reading from that to influence the flow temp used.

The system is usually configured with a heat loss "curve" that maps the external temp to a flow temp. The installer will select a curve that reflects the thermal performance of the building.

Well worth tweaking these. After a few days look at the graphs that record temps over time.

Why bother. She can just twist the valve or tap the thermostat for a boost..

Dave

Strictly speaking, more efficient at lower return temperatures. That’s what is needed to recover heat energy from the exhaust.

Tim

Just over a year later and a couple of months out of guarantee and first issues of any consequence of arisen.

Prior to this the installation worked fine over last winter and to date. The Wiser app on Android for the most part was trouble free and enabled schedules to be setup for any day of the week. As we are both retired there was no need to make any weekend alteration and so one day's schedule was setup and then copied to the rest of the week.

A couple user defined shortcuts allow to turn off till next time event or boost till next timed event.

I've not done a detailed year/season comparison yet and clearly just looking at bills isn't useful. My gut says I've saved money. We have a large south facing lounge in which the thermostat resides (out of direct sunlight) so the heating turns off sooner than I'd like in the study at the back of the house.

Anyway that was all up till last night when my wife knocked the thermostat on the coffee table and it toppled over, still on the table. Since then the whole system has been unstable. Funny thermostat temperatures, boiler (Baxi 105HE) stopping with fault light

I've reset the boiler with the reset switch, reset the boiler and thermostat control unit by turning off the power, removed the batteries from the thermostat, put back and attempted a reset, all more than once. Things seem more sensible since the last time I did the resets (swapped the batteries around though the display shows they are good).

If the issues continue I am minded to take the thermostat out of the loop and wonder what is the easiest way to do that, eg do I just short across the "call for heat" connections? If faults continue then I can put it down to the boiler which is on my list to replace next summer anyway. Note the boiler has its own timer module which at the moment is set to follow timer and all timer pins are OFF (so the Call for heat is made by the Drayton control unit).

The fault light on the boiler does not sound like something that could be as a result of anything related to the stat. I suspect you have unrelated fault that has shown up at the same time by coincidence.

Could it be as simple as the system pressure is low? What does it say on the pressure gauge?

I don't like "coincidences". The one day x happens y also happens despite a year of operation (ok not much happend over summer).

The boiler kicked in as expected this morning, ran all day in accordance with schedule then at 1845 stopped again. Simply turned the Boiler On/off/Hot water only dial to off, then on again and boiler fires up. Pressure ~1.5 bar on restart (pipes still warm), and some

Can you posit a way in which doing something with the call for heat on the boiler could result in a pressure / pump warning?

The don't seem like plausibly related things, hence my desire to not attach significance to them in association.

Are you sure your expansion vessel is suitably charged? If you're going to drop the system pressure now is a time to check and perhaps recharge?

Regarding the "plausibly related things" my gut tells me that if something happens to make the boiler work harder then the boiler will fail. I had this last winter when I took the thermostat from the moderately warm lounge in the front (south facing/large window) to my study in the back and the boiler was unable to get my room up to temperature and then failed. I reset and put the thermostat back in the lounge. On the recent occasion my wife in her "panic" to put the dislodged thermostat back had I think it the + button a few times upping the target temperature from 19.5deg to 23.5deg and I suspect that had a similar issue to moving the thermostat to my study, the boiler/boiler settings did not allow that temperature to be reached.

FWIW I gave the boiler interior (not the burner) a bit of clean, cobwebs, spider skins, and brushed some of the crud off of the DHW sensor. I also dropped the pressure (at cold) from 0.8 to 0.6, didn't want to go any lower.

Whilst the boiler worked fine for a day the room was not reaching target temperature so I turned the control up from the 4 'o' clock position to 6 'o' clock. Here is where strange things happend. At the 4 'o' clock position the neons (in 10deg increments starting at

System ran last night all right until again 8am with the fault light flashing. Reset and back up running until not needed at 1030.

An hour later I decided to have a shower and that was a nightmare. Ran, then hot, then off. This happened a couple of times, fault light flashing then after a few moments back on again until after about the

So this afternoon, I decided to have another go at reaching the target temperature and turned the dial to 4.5 'o' clock. It took about

I observed a couple of cycles:

1. Approx 5’30” on, neons at 60°
2. ~ 3 mins no burner then pump off
3. Fault light flashes, 3 neons, then another 1” before cycle restarts

I'm sure I've read that it is better for the burner to cycle than be constantly on. Does the cycle ratio on/off seem reasonable? Last year I had the boiler temp too low and got a lot of short cycling/hunting.

I feel that there is a sensor fault and/or the temperature dials are an issue. The pump gets more than hand hot which is a bit of a concern.

I'm hoping that I can get the boiler to limp through this winter with the intention of replacing it next summer. Trying to get a man in to have a look but of course they are all a bit busy with people like me!!

Depending what you mean by "work harder". An oversized boiler that does lots of cycling will likely fail before one more appropriately sized for the heating load. But decent length firings at whatever temp you have selected are the least "wearing" use pattern.

or possibly the radiator output vs. the rate of heat loss from the room...

IME boiler pressure warnings are not complaining about higher than expected pressure, but lower pressure. A sealed system boiler will include an over pressure relief valve to vent water outside should the pressure ever get too high - so it is not something most boilers would report as a fault code. A low pressure reading however will get reported. Generally you would set the pressure at the boiler to between

What temperature are the neon indicators reporting - flow or return? If reporting the return temp then it is entirely possible that you get temperatures reported that don't necessarily match what you have set as a target flow temperature, since the heating load can vary significantly from one time to another.

Combis will normally give priority to DHW - so even if the heating was on, drawing DHW will in effect turn off the heating for the duration.

You can get temperature fluctuation problems with some combis at low rates of DHW demand since the boiler may not be able to keep within the specified max DHW flow temp - even when modulated down (assuming it is a modulating boiler) to minimum output. At that point the only option that have is to cycle off.

What make / model of boiler is it?

With a modern condensing boiler I would say the reverse is true. The ideal situation is to have it run with nice long burns with its output modulated such that it closely matches the heating load. That places least wear and tear on the boiler (less thermal cycling, less valve operation, less stress from ignition, fan proving etc), and gives a nice stable room temperature with no overshoots. It also maximises condensing efficiency, since lower return temperatures will allow greater latent heat recovery.

Here is where the type and level of sophistication of the boiler will come into play.

On old fixed output boilers, the temperature "control" was basically just a thermostat, that would set the temperature at which the burner would stop firing. So if you turned it down it would (crudely) lower the average flow temperature by cycling the burner. Generally it is better to have them set fairly high since you are not going to gain any condensing efficiency at lower temperatures, and if it did start condensing then it would cause accelerated corrosion in the boiler anyway.

On more modern modulating boilers the flow temp will set a desired output flow temp. The boiler will then run at high output until that flow temp is achieved, and then start to reduce output power to maintain it at that level. As the house warns and the return temp increases, then they will modulate down further. If there comes a point where the heating load is so low that the flow temp would exceed what you have set even with the boiler at its lowest output power, then it would behave like the older fixed output boiler and cycle on the internal stat.

Possibly - but understanding what they do and what they are trying to tell you would also be handy :-)

Well it is made out of conductive metal, and has heated primary flow water running through it. So you would expect it to be has hot as the water it is pumping really - so that could easily be 60 to 80 degrees, and definitely not "hand safe" to touch.

Yup, first really cold snap of the year is never a good time for that kind of stuff. (as I found to my cost just trying to get a recon PCB for mine last year)

Some manufactures seem to recommend something between 1 and 1.5 bar when cold. As you say, there is a (over) pressure relief valve set to around

If the boiler is oversized, which seems to be common when a like for like boiler replacement has been undertaken without re-evaluating the heat loss of the house, the boiler often cannot modulate down far enough and will always short cycle. Modern boilers do tend to have lock out periods to try and minimise the shortness of the cycle. After the flow temperature is exceeded on the lowest boiler modulation the burner will turn off. The boiler then locks out for x number of minutes before it will fire up again. The pump continues to run during this lockout and the flow temperature may drop quite a way below the set temperature before the boiler fires up again. The boiler will always fire up at the highest burner rate before modulating down.

If the OP has set the flow temperature too low on an oversize boiler then he is possibly running into this lockout period. It may be better for heating comfort and boiler opperation to set a higher flow temperature rather than slavishly following the generic advice to have a <60C flow on a boiler that doesn't run efficiently with a lower flow temperature

When replacing an old boiler don't assume that the new boiler needs to have the same heat capacity as the old boiler. The house may have been improved with double glazing or better insulation in the intervening years. Perhaps 10 or 20 years ago the heating "engineer" may have performed a house heat loss calculation and just added x2 factor for the boiler specification. With modern condensing boilers its better to match the boiler more closely to the house heat loss or select a boiler with a much better modulation range.

I'm trying to posit a way in which it doesn't happen :)

See response below.

If I get a new system in I'll have the radiator sizes and balancing re-checked. I think my study radiator, against and outside wall in a flat roof extension, is undersized. But the boiler, in trying to get to an unachievable temperature, ended up with the fault light so there was a weakness then.

See response below. I don't think the pressure is, or has been, out of bounds, either cold or operating (currently at about 2bar when running).

Flow as best I understand it, see response below.

As I understand it the boiler will not modulate low enough. A more modern one will.

I don't think this boiler will modulate enough to be running continuously. I went through this last year (thread somewhere in this NG) and it was ascertained that at the lowest modulation (6kW?) it would still need to cycle.

That makes sense.

Thanks again for your input and some responses in-line above. I suspect some historical postings with basic information have got lost in broken threads. By "working too hard" I mean the boiler output temperature is too low to attain the desired room temperature so the burner is on continuously.

The shower issue arises it seems to me (not proven) when the whole boiler starts from cold and it will cut out, for whatever reason, until the boiler has reached a steady working temperature. It took about 10-15mins before the shower ran nicely for me yesterday.

Boiler is a 2006 (manufacture) Baxi 105HE combi.

As best I understand the temperature sensor is on the Heat Flow pipe. The pump is on the Heat Return pipe and before the burners.

The Neons are 30° 40° 50° 60° 70° 80°

Boiler temperature is set by the dial mentioned earlier and is currently just after the 4 'o' clock position. A little bit lower and the room temperature is not attained. At its current position I get the cycling mentioned earlier. If I go to after 5 'o' clock something goes wrong the the delivery temperature only reaches 40°.

The boiler also has the optional integral timer. Before I put the room thermostat unit in last September then that is how the house was controlled with my running down to the boiler to increase/decrease the boiler temperature as needed, ie wind up if going to be cold, wind down if warm or we were out for a couple of days.

The pressure relief valve was replaced a couple of years ago. Nothing wrong with it until the engineer ignored the "do not drain via the pressure relief valve" warning when changing the diverter valve.

The boiler worked fine from yesterday 0800 until this morning at approx 0850 when the 60° neon was flashing again and the boiler stopped.

The neon indicates "Fault on Pump or Low System Pressure" The system pressure was higher when all this problem started, initiating my post on 28 Nov.

I'm merely working on changing what I can and is easy. Any more than that I need a man in.

I'm minded to try disconnecting the room thermostat/hub system and reverting to how it used to be with the integrated timer.

However if all I need to do to get through the winter is turn the boiler control dial to Off and the On again then I could live with that as it is something I can also instruct SWMBO to execute.

IME/IIUC, it all depends on what you try to do. 'Low enough' will be too high for 2 or 3 decent sized radiators. If you're only heating one smallish room I'd have thought an electric heater would be best. A modern gas boiler will simply not modulate down to a low load.

Well that is quite easy - your boiler has a fault - although marginal as it is not stopping it completely. It seems that any prolonged period running, or any period of inactivity is causing it to not work as it should. The stat may be the thing that set when and for how long it works, but that is not going to be the "cause" of the fault - just a trigger. Likely you would see the same result with the stat replaced by a loop of wire.

I don't think the boiler "cares" whether it s being asked to do something unachievable - it just runs in response to a call for heat, and operates within the parameters that have been set like flow temp, and heating load. It should run reliably 24/7 if requested to do so.

I was more curious why you felt the need to lower the system pressure? The manual shows the minimum system pressure as 0.5 bar. The pressure relief is set at 3 bar.

One of the lights on the front has the description "Fault on Pump or Low System Pressure" - so definitely not an over pressure indication.

The manual has this to say on anti-cyling etc:

Central Heating Mode (Fig. 2)

1. With a demand for heating, the pump circulates water through the primary circuit. At a pre-determined flow rate the central heating flow switch operates, initiating the ignition sequence.
2. The main burner ignites at low rate, then the gas valve controls the gas rate to maintain the heating temperature measured by the temperature sensor.
3. When the flow temperature exceeds the setting temperature, a 3 minute delay occurs before the burner relights automatically (anti-cycling). The pump continues to run during this period.
4. When the demand is satisfied the burner is extinguished and the pump continues to run for a period of 3 minutes (Pump Overrun).

The minimum on that boiler appears to be 11kW which is fairly high.

Also if in a hard water area, scaling in the DHW plate heat exchanger can cause issues with power transfer to the water.

Yup ok... just a case of unrealistic settings for the circumstance With manual control of the flow temp, then you will need to make adjustments for the colder parts of the year.

So a boiler fault by the sounds of it.

You may still need to do that with a stat - since the stat is only controlling when it is asked to run, not at what temperature to run. (you need a weather compensator[1] if you want automatic control of that)

Yup, better not to operate them at all if possible.

The pressure gauge should eliminate one of those easily enough, so chances are you have a faulty pump or flow sensor.

Might have to look at replacing a Boiler as a heat pump won't hack it;! and to that end anyone know of a good heat loss boiler size calculator as i thing this boiler was too big originally!..

Cheers..