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Thread: Tracking down random boiler demand with Evohome

  1. #21
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    Quote Originally Posted by G4RHL View Post
    I agree they should not occur but I suspect that whilst many approved installers can do the wiring and if required install TRVs most probably do not have the knowledge about the sequence to fully bind it all and what to do. Elsewhere we have a topic dealing with things to put in the manual but the best advice I have seen is that from The Evohome Shop elsewhere in the forum telling you blow by blow, with no ambiguity, about what you do. Follow it and there ought not to be an issue. Of course this assumes the wiring is correct!
    Maybe the mods could make the full unbinding/rebinding advice a sticky?

  2. #22
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    Just to muddy the waters further, I suffered from the plague for a random call for heat from a BDR91. Tried completely resetting it, along with the Evohome controller with no success. Eventually it started to throw the "COMM ERROR" during the night which others have mentioned. Richard at The Evohome Shop very kindly replaced it under warranty and it's been absolutely faultless since.

    So it might not be you!

  3. #23
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    ...and I could not put my temperature sensor into action when first bought. Our well mentioned source of information on this forum knew the answer - take out the circuit board and slightly bend the contact for the battery to make contact with the board. So yes we do have manufacturer's defects from time to time. Not a lot!

  4. #24
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    Quote Originally Posted by G4RHL View Post
    ...and I could not put my temperature sensor into action when first bought. Our well mentioned source of information on this forum knew the answer - take out the circuit board and slightly bend the contact for the battery to make contact with the board. So yes we do have manufacturer's defects from time to time. Not a lot!
    Glad my tip worked!

    Lets face it no matter how well items are made, nothing is faultless (hence I always use to take two of everything in my van when I was on boiler breakdowns as there was every possibility the new part could be faulty too!).

    Out of thousands of evohome products we have sold I can put my hand on my heart and say we have had very few returns. As Fursty Ferret has mentioned, we really do try and sort things out as quick as we can with anything that is suspected as being defective.

  5. #25
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    Hi all,

    I'm experiencing random calls for heat as well, I have an OpenTherm R8810 in place as a boiler relay and in the beginning I was thinking I had a faulty unit - but, reading on, I see more and more occurrences in which there's something wrong firing the boiler.
    My installation is quite simple. One HR92 was used for testing but I deactivated it (deleted zone on controller, removed batteries from HR92) when I put everything actually to work.
    I have two zones, with motorised zone valves driven by two BDR91s.
    One zone is bound to the central controller as a sensor. The other one uses an DTS92 (I bought an DT92as an addendum for my EvoHome CC kit and I'm using the wireless thermostat DTS92 and the relevant BDR91 in the same zone, after resetting both).
    I started out without a boiler relay, connecting my boiler to the zone valves'switches. With that setup, everything used to work fine.
    Now I added the R8810 and the random boiler demand issue came up:
    - it happened more than once that both my zone sensors were reaching the setpoint from below (say they were 19C with a setpoint of 20), the EvoHome turned the boiler off and the temperature began decreasing and went to 18C before the boiler was fired again. It took more than one hour. I was home but refrained touching anything because I wanted to understand what was going on. I observed both zone valves were open (green light on BDR91s) as expected, but it appeared as the EvoHome "forgot" to fire the boiler.
    - it happened more than once as well that my boiler was firing and at the same time both the zone valves were shut, because both zones were above setpoint. It's okay to have a temperature curve and to try predicting temperature loss, BUT IMHO when the controller calls for heat it MUST open the valves at the same time, otherwise it would result in an unnecessary boiler water overheating and bypass firing. When it happens at night, it always wakes me up because of the noise my boiler makes when overheating and activating the internal bypass.
    Now, since I read these pages, I'm aware of binding-related issues, so I actually rebound everything more than once, wiping configuration and rebuilding from scratch. Issues arose back again unchanged after everything had been reconfigured. This could mean I'm just making the same mistakes again of course, but I still can't understand why it seems to involve the heat demand part only. If I rely the heat demand on zone valves switches, and delete the binding with the R8810, everything works fine. I can't figure out what kind of binding issue/conflict could it be, since the "malfunctions" is not constant: 8 times out of 10, my EvoHome calls for heat at the right moment. If I tap a quick action, the boiler responds almost immediately switching on or off, unless the system is already in one of the "deadlocks" I described earlier (in which case sometimes I had to switch boiler off and back on).
    I tried rebinding my R8810 and it appeared to fix the issue - but in a few days it came back. It might just have reset some parameters in the controller?
    As I said earlier, I tried resetting every single component in my system (controller, R8810, two BDR91, one DTS91, left out the one HR92) and rebuilding/rebinding everything. Ditto, issue was back in a few days.
    OpenTherm communications between R8810 and my boiler seem OK (I placed an OpenTherm gateway in between and it's recording no faults). Can't say the same for the communications between R8810 and the controller, but they are 5 meters away from one another, line-of-sight, no obstacle in between, no metal objects within 30cm and the RF test results in 5 red blinks. Despite this, the EvoHome error log shows a 10 minutes connection loss. It behaves like it sometimes misses a beat... If it misses the beat that switches the boiler on or off it could explain erratic behaviour. It doesn't seem a binding issue... am I wrong? Something I didn't try?

  6. #26
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    Quote Originally Posted by emmeesse68 View Post
    - it happened more than once as well that my boiler was firing and at the same time both the zone valves were shut, because both zones were above setpoint. It's okay to have a temperature curve and to try predicting temperature loss, BUT IMHO when the controller calls for heat it MUST open the valves at the same time, otherwise it would result in an unnecessary boiler water overheating and bypass firing.
    Could not agree more, in a well-engineered industrial system you would wait for confirmation that the valves were open before firing the boiler. Is it possible with your boiler to use the R8810 for proportional control and also have the end switches as an over-ride?

    Otherwiser it sounds like you would do well to claim a refund on the R8810 and revert to using the end switches on their own. Because of their internal design it's virtually impossible for the switch to be activated if the valve is not open.

    On a related point I have just upgraded to a colour controller and I think the behaviour is subtly different from the monochrome one. Previously the BDR91 kept the boiler firing and pump running until all the HR80 valves were completely shut, now it seems to turn them off when the valve travel has got to about half-way.

  7. #27
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    Quote Originally Posted by sharpener View Post
    ... Is it possible with your boiler to use the R8810 for proportional control and also have the end switches as an over-ride?
    Don't think so, OpenTherm works on a continuous basis, and doesn't allow for switches in between... It's a two-way protocol that makes a master unit (usually a thermostat) control a slave unit (usually a boiler) while the boiler powers the thermostat through the same two-wires line. Putting a switch in between would actually stop the boiler but would also cut the power to the thermostat (the R8810 in my case).

    Quote Originally Posted by sharpener View Post
    Otherwiser it sounds like you would do well to claim a refund on the R8810 and revert to using the end switches on their own. Because of their internal design it's virtually impossible for the switch to be activated if the valve is not open.
    End switches are failsafe, but I'm planning to change structure, in fact I ordered some HR92 radiator valves (being delivered tomorrow morinig) to replace one of the two zones, and in that case I'll need some way to let my EvoHome call for heat directly. One possibility is the R8810 (OpenTherm modulating controller) that I'm using at present, another is a BDR91 (on/off boiler relay) that I can take from the zone valve I'm not using anymore, to check if the problem is in my R8810 or it's a bug in EvoHome's controlling algorithm.
    And I'd like not to lose the modulating function of my OpenTherm boiler by driving it with an on/off switch...

  8. #28
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    Quote Originally Posted by emmeesse68 View Post
    Don't think so, OpenTherm works on a continuous basis, and doesn't allow for switches in between... Putting a switch in between would actually stop the boiler but would also cut the power to the thermostat (the R8810 in my case). And I'd like not to lose the modulating function of my OpenTherm boiler by driving it with an on/off switch...
    I had in mind leaving the end switches connected across the timer terminals on the boiler (presumably you have replaced this with a link now). I've checked with the instructions for my Vokera boiler and it looks as though you could either do that, or connect them in place of the link on the low voltage board where the optional underfloor limit stat and/or condensate pump alarm would go (subject in theory to the Part P regulations about mains and low voltage cables in the same trunking etc.)

    BTW how do you stop the Opentherm stat turning down the boiler while there is a demand for hot water? (I had a similar problem with the weather compensation which I solved with a relay that open-circuits the OAT sensor.)

  9. #29
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    Quote Originally Posted by sharpener View Post
    I had in mind leaving the end switches connected across the timer terminals on the boiler (presumably you have replaced this with a link now). I've checked with the instructions for my Vokera boiler and it looks as though you could either do that, or connect them in place of the link on the low voltage board where the optional underfloor limit stat and/or condensate pump alarm would go (subject in theory to the Part P regulations about mains and low voltage cables in the same trunking etc.)
    Actually OpenTherm allows a switch to be connected in place of a modulating thermostat (to allow for an on-off controller to be connected in place of an OpenTherm one), thus many OpenTherm-enabled boilers allow to connect a classical on/off timer/thermostat OR a remote OpenTherm unit to the same wires. My Ferroli BlueHelix Pro came with a link that I had to replace with the wires that used to be connected to my valves' end switches, and now are connected to the R8810. So, in my case at least, I don't have an extra connection for an override switch on the boiler.

    Quote Originally Posted by sharpener View Post
    BTW how do you stop the Opentherm stat turning down the boiler while there is a demand for hot water? (I had a similar problem with the weather compensation which I solved with a relay that open-circuits the OAT sensor.)
    As far as I understood, my boiler (it's a combi CH + DHW) can provide only CH or DWH at a given time, not both. So, when it's providing heat to radiators AND I open a hot water tap, it switches to DHW and stops circulating radiators. In such a circumstance, EvoHome has to be configured for "NO hot water" option. The boiler would control it all.

    If you have the hot water option installed, I guess it's different - but I have no experience of such a configuration.

    As of external temperature compensation, I have an outside temperature sensor attached to my boiler but I didn't set it up yet (I tried in the past when I was using end switches and deactivated it when I added the R8810 to keep the design simple, as if it helped understanding how it works). I'm planning to check it out when I'm settled with the rest...

  10. #30
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    Quote Originally Posted by emmeesse68 View Post
    My Ferroli BlueHelix Pro came with a link that I had to replace with the wires that used to be connected to my valves' end switches, and now are connected to the R8810. So, in my case at least, I don't have an extra connection for an override switch on the boiler.
    I get the picture now

    Quote Originally Posted by emmeesse68 View Post
    As far as I understood, my boiler (it's a combi CH + DHW) can provide only CH or DWH at a given time, not both. So, when it's providing heat to radiators AND I open a hot water tap, it switches to DHW and stops circulating radiators. In such a circumstance, EvoHome has to be configured for "NO hot water" option. The boiler would control it all.

    If you have the hot water option installed, I guess it's different - but I have no experience of such a configuration.
    I have a conventional system boiler but the HW is still controlled by the original timer and S-plan zone valve. The Evotouch controls the heating using a BDR91 configured as a boiler relay, operating the CH zone valve via the original timer's CH contacts so we still get familiar push-button functions like AUTO, ALL DAY and CHANGE.

    Everything can also be over-ridden by an Aviosys control box connected to my internet router, this gives me access from anywhere with a standard browser so no Honeywell servers or apps involved. It has in-built timers to control the (largely obsolete) underfloor heating, and also to enable the radiator heating for frost protection from 0200 to 0500 when all the TRVs are set to 5.0C. So like you I am keen to avoid spurious calls for heat in the middle of the night!

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