Results 1 to 9 of 9

Thread: Heating system in security mode "Error" because of EvoHome (T2 - T1 > delta max)

  1. #1
    Automated Home Sr Member
    Join Date
    Apr 2016
    Posts
    66

    Default Heating system in security mode "Error" because of EvoHome (T2 - T1 > delta max)

    Hi there,

    I would like to get your opinion related to this issue I have.
    My ACV heating system is times to times getting an error message "B30" which means "T2 - T1 > delta max", meaning the delta between departure "hot" water temperature and return "cold" water is too big. In other words that means that the heating system is sending hot water but returned water is to too "cold", ... and that happens when only 1 or 2 of my 9 heaters are used, and linked to the fact that the HR92 is not opened enough, and therefore there is not enough "hot" water coming back to the heating system.

    The issue is not happening when I open most of my HR92's, or I replace one of my HR92's by a standard thermostats valved open at 100% for example.

    I would like to know if this makes sense and if there is a setting to be done on the HR92 so that for example it opens quicker than usual when there is heating demand for example ?

    Many thanks !

  2. #2
    Automated Home Legend
    Join Date
    Sep 2014
    Location
    Scotland
    Posts
    2,291

    Default

    Quote Originally Posted by morpheus View Post
    Hi there,

    I would like to get your opinion related to this issue I have.
    My ACV heating system is times to times getting an error message "B30" which means "T2 - T1 > delta max", meaning the delta between departure "hot" water temperature and return "cold" water is too big. In other words that means that the heating system is sending hot water but returned water is to too "cold", ... and that happens when only 1 or 2 of my 9 heaters are used, and linked to the fact that the HR92 is not opened enough, and therefore there is not enough "hot" water coming back to the heating system.

    The issue is not happening when I open most of my HR92's, or I replace one of my HR92's by a standard thermostats valved open at 100% for example.
    No answers at the moment but I have some questions:

    1) What is delta max set to on the boiler ?
    2) Is the pump an automatic (load sensing) variable speed pump or a fixed speed pump, if the latter which speed is it set to ?
    3) Is there an automatic bypass valve installed in the system and if so do you know what differential pressure it's set to ? (Most let you adjust between 0.1 and 0.6 bars)

    I would like to know if this makes sense and if there is a setting to be done on the HR92 so that for example it opens quicker than usual when there is heating demand for example ?
    No, there's no setting like this on an HR92 which would help your situation. If the HR92 was to open "quicker" or more than necessary that would cause the room temperature to overshoot. It opens the amount it needs to and no more.

    Keep in mind that the heat demand signal which causes the boiler to fire ultimately comes from the HR92's in the first place - they don't call for heat unless they are opening their valve.

  3. #3
    Automated Home Sr Member
    Join Date
    Apr 2017
    Posts
    98

    Default

    If you have a bypass valve in your system, you could try easing it off until a suitable return temp is achieved.


    Martin.

  4. #4
    Automated Home Legend
    Join Date
    Sep 2014
    Location
    Scotland
    Posts
    2,291

    Default

    Quote Originally Posted by blowlamp View Post
    If you have a bypass valve in your system, you could try easing it off until a suitable return temp is achieved.
    Indeed, it sounds like there is no automatic bypass valve as if there was one then only one or two radiators opening slightly would cause most of the flow to go through the ABV causing a very low differential rather than the "excessive" differential seen here.

    However if it's a load sensing variable speed pump you can't necessarily use an automatic bypass valve with it, in that case it might be necessary to increase the allowed differential on the boiler or configure some other boiler settings.

    It's not something that any settings on Evohome can solve anyway.

  5. #5
    Automated Home Sr Member
    Join Date
    Apr 2016
    Posts
    66

    Default

    Hello, I am not sure what is the delta max which is set (this is all electronic device), nor the kind of pump I have (I only know I have a circulator for hot water, and a second circulator for heating system), but on the installation diagram I notice this item in "1" which is not present in my installation :

    Capture d’écran 2020-12-28 à 17.19.10.jpg

    This is definitively not present in my installation ... bu tis it a simple pipe between departure and arrival ?
    Do you know what kind of device is this "1" ? if you would have a picture of it so that I would know what I need to buy ?

    many Thanks !

  6. #6
    Automated Home Legend
    Join Date
    Sep 2014
    Location
    Scotland
    Posts
    2,291

    Default

    Item one is almost certainly an automatic bypass valve.

    This is a spring loaded one way valve which will remain fully closed until a pre-set pressure differential is reached before it begins to open and allow flow - at that point it will try to regulate the pressure differential to the set level by opening further as the pressure increases. Think of it like an adjustable pressure relief valve.

    One side is connected to the flow side after the boiler and pump but before any zone valves, (so that a zone valve cannot isolate it) and the other side is connected to the return just before the boiler.

    The differential pressure can usually be adjusted between 0.1 and 0.6 bars to suit the system, I think I have mine set at 0.5 bar but I'd have to check.

    The idea is you want it set high enough so that when at least 2-3 radiators are open there is no flow through the automatic bypass valve, (and all the flow goes through the radiators) but when you are down to only one or two radiators partially open and there is not enough flow for the boiler the valve will open and provide a bypass path for some of the water to flow.

    In your situation this would prevent nearly closed radiators from causing an excessive differential temperature.

    They are readily available, I think the following is the valve I fitted in my system: (or very similar to it, it's been several years since I fitted it)

    https://www.plumbnation.co.uk/site/h...e-22mm-angled/

    It's a 22mm right angle type - 22mm because that's the pipe size out of my boiler. You can also get straight through types and types for other pipe sizes like 28mm. It must be installed the right away around as it is directional.

    Installing one is probably going to require the system to be drained down, main supply and return pipes cut and a couple of T joints soldered in place to go to the valve - this is how I installed mine.

    Before you fitted Evohome did any of your radiators have no TRV on them like a hallway or bathroom radiator ? If so, the system probably relied on them as a "bypass radiator" which always allows some flow, and I think this is quite common on old systems as you can get away without an automatic bypass valve if there is a permanently on bypass radiator.

    In our house the hallway radiator had no TRV and acted as the bypass radiator and there was no automatic bypass valve in the system.

    However if you then add Evohome TRV's to all radiators including the one which was previously a bypass radiator - as I did, an automatic bypass valve needs to be installed. If you're not reasonably confident in soldered plumbing work on a heating system you may want to get a heating engineer in to install it for you. I would probably set it to about 0.5 bar as a starting point and see how it goes.

    A correctly set automatic bypass valve can also help quieten radiators that are noisy when only one or two radiators are open - they become noisy because the differential pressure gets too high, the automatic bypass valve sets an upper limit on how high the differential pressure can get under any circumstances.
    Last edited by DBMandrake; 28th December 2020 at 06:14 PM.

  7. #7
    Automated Home Legend
    Join Date
    Jul 2014
    Posts
    1,503

    Default

    This is a common problem with boilers. My 38KW Vaillant boiler used to do this all the time. Boilers are sized for the house, but with Evohome, the house is rarely being heated at the same time. My only solution was to derate the boiler and now its running as an 18KW boiler and all is fine.

  8. #8
    Automated Home Legend
    Join Date
    Sep 2014
    Location
    Scotland
    Posts
    2,291

    Default

    Quote Originally Posted by bruce_miranda View Post
    This is a common problem with boilers. My 38KW Vaillant boiler used to do this all the time. Boilers are sized for the house, but with Evohome, the house is rarely being heated at the same time. My only solution was to derate the boiler and now its running as an 18KW boiler and all is fine.
    Would you agree that an automatic bypass valve is still required though ? I assume you have one ?

    If the system was originally installed with a bypass radiator and no automatic bypass valve and all radiators are controlled now the pump and boiler will not be happy at all and could even be at risk of damage when the flow is restricted too much.

  9. #9
    Automated Home Legend
    Join Date
    Jul 2014
    Posts
    1,503

    Default

    100% an automatic by-pass is needed and infact with Evohome becomes mandatory. I also have my towel rails by design with no TRVs.
    Even with these, if you have a large boiler and only a small heat demand, you can run into the temperature differential problem. That's when de-rating the boiler was my only solution, beside installing a Low Loss Header loop.

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •