Evohome - fine tuning controls

[Midori]

My boiler (Vaillant 418) is gas fired heat only open vent type. Burner start-up sequence to confirm electrics, pump running, fan pressure correct and open gas valve takes around 50 seconds. So when the Evohome relays open and close for one minute or so, my boiler gets abused real bad. There is no time for the burner to do its work and, even though there is a water pump run on period, the water is not heated anyway, the pump runs 100% thru bypass because zone valves are closed, and the rads stay cold of course. So every 10 Evotherm cycle minutes my burner gets abused and the rads get colder. I have to solve it or buy another manufacture's control product.

If you are saying the default EVO cycle is 6/hr (10 mins), that is what I have set (see above). I dissagree the MIN ON TIME (1 to 5) set at 1 minute is correct. Not only will it knacker my boiller, but also wear out the motorised valves earlier, after intial warm up, and the rads will get colder and colder each cycle. And it is a waste of gas! Perhaps I misunderstand Honeywell's purpose for Min On Time set 1 minute. Is it to pulse elecronic radiator valves (not fitted in my case) whilst the pump and boiler stays running?

If you look at Honeywell evohome Installation Guide: Sample evo systems:
I have the S Plan two-port valves installed as page 42, except there is an additional heating zone.
A bypass is also fitted for when all motorised valves are shut.
Wiring is exactly as circuit on page 46 except pump is allowed to overun under supervision of boiler.

Obviously the "DHW BRD" on page 46 stays ON for a considerable period, then off for a considerable period, but why isn't EVO holding each of my two "HTG BRD's" ON for 5 minutes as set in "MINIMUM ON TIME" ?

[top brake]

If you look at Honeywell evohome Installation Guide: Sample evo systems:
I have the S Plan two-port valves installed as page 42, except there is an additional heating zone.
A bypass is also fitted for when all motorised valves are shut.
Wiring is exactly as circuit on page 46 except pump is allowed to overun under supervision of boiler.

Obviously the "DHW BRD" on page 46 stays ON for a considerable period, then off for a considerable period, but why isn't EVO holding each of my two "HTG BRD's" ON for 5 minutes as set in "MINIMUM ON TIME" ?

because you do not have a boiler relay and these options are not enabled

[paulockenden]

Midori, I suffer from this too. When the system is in the TPI band Evohome will short-cycle my boiler such that it doesn't actually come on. It's a terrible waste of energy. It also means that when heat really is needed the boiler takes even longer to fire up - maybe because the combustion chamber gets flooded with unburned gas?

A couple of observations: 1) With an S=Plan setup it's even worse because you don't have access to the boiler cycle parameters in the Evohome interface. 2) At least this ONLY happens when the house is relatively up to temperature, and one of the zones is demanding heat in the TPI (proportional) band.

What Evohome really needs, across all configurations, is a setting that says "My boiler takes xx seconds to ignite". It currently seems to make assumptions about that which aren't necessarily sensible.

In fact, I've been thinking about making a small box of tricks that holds the two port valve open for an additional 45 seconds of so after the BDR91 goes off.

P.

[Midori]

Midori, I suffer from this too. When the system is in the TPI band Evohome will short-cycle my boiler such that it doesn't actually come on. It's a terrible waste of energy. It also means that when heat really is needed the boiler takes even longer to fire up - maybe because the combustion chamber gets flooded with unburned gas?

A couple of observations: 1) With an S=Plan setup it's even worse because you don't have access to the boiler cycle parameters in the Evohome interface. 2) At least this ONLY happens when the house is relatively up to temperature, and one of the zones is demanding heat in the TPI (proportional) band.

What Evohome really needs, across all configurations, is a setting that says "My boiler takes xx seconds to ignite". It currently seems to make assumptions about that which aren't necessarily sensible.

In fact, I've been thinking about making a small box of tricks that holds the two port valve open for an additional 45 seconds of so after the BDR91 goes off.

P.

@Paul.... Glad to see it is not just me. I too thought about installing two normally closed timed open (NOTO) relays to extend BRD short cycling, but they are not so cheap to buy and you risk confusing the rogue EVO firmware even more. The EVO seems to have errors if the onboard thermo sensor cannot integrate itself in "co" mode like the Y78RF does. The bhe basic EVO control loop is poorly conceived or buggy if it ignores MIN ON TIME criteria for each zone output signal.

Seems I am faced with anther £85 bill to try and see if the issues resolve by adding a boiler relay and remote sensor. Or to buy & fit two or three NOTO relays and have a lash up system. If the EVO has no facility for updating firmware to overcome bugs, then best way forward may be to start over with another system. I shall await a few more replies before deciding where to put my money. I much prefer to get what I paid for initially and what was clearly stated in the user instructions that came with my "new version" EVO.

[top brake]

@Paul.... Glad to see it is not just me. I too thought about installing two normally closed timed open (NOTO) relays to extend BRD short cycling, but they are not so cheap to buy and you risk confusing the rogue EVO firmware even more. The EVO seems to have errors if the onboard thermo sensor cannot integrate itself in "co" mode like the Y78RF does. The bhe basic EVO control loop is poorly conceived or buggy if it ignores MIN ON TIME criteria for each zone output signal.

Seems I am faced with anther £85 bill to try and see if the issues resolve by adding a boiler relay and remote sensor. Or to buy & fit two or three NOTO relays and have a lash up system. If the EVO has no facility for updating firmware to overcome bugs, then best way forward may be to start over with another system. I shall await a few more replies before deciding where to put my money. I much prefer to get what I paid for initially and what was clearly stated in the user instructions that came with my "new version" EVO.

You don't need to buy another relay. Simply reassign the heating valve relay as a boiler relay, wire directly to the boiler and latch open the heating 2 port valve. Hey presto control of minimum run time.

It is covered in manual and youlearn.

[Midori]

You don't need to buy another relay. Simply reassign the heating valve relay as a boiler relay, wire directly to the boiler and latch open the heating 2 port valve. Hey presto control of minimum run time.

It is covered in manual and youlearn.

Yeah! It all became patently clear when I re-read all the advice I received on this subject.
My bindings are incorrect from start, or became corrupted, because Min ON TIME should not appear in Evo menu system.
I have to implement BOILER RELAY control in order to have Min ON Time available in the menu system.
I have to Factory Reset Evo, remove Evo batteries for a while, fix up new wiring relays to boiler, un-bind all devices, and rebind the lot with care

I am gona do it! May take me a couple of weeks to complete !

Many thanks to all that commented.

[paulockenden]

You don't need to buy another relay. Simply reassign the heating valve relay as a boiler relay, wire directly to the boiler and latch open the heating 2 port valve. Hey presto control of minimum run time.

It is covered in manual and youlearn.

Has the manual changed then? Because when mine was installed last year it said that for an S-plan system the correct configuration was a relay for each two port valve, and none on the boiler.

P.

[morfsta]

You don't need to buy another relay. Simply reassign the heating valve relay as a boiler relay, wire directly to the boiler and latch open the heating 2 port valve. Hey presto control of minimum run time.

It is covered in manual and youlearn.

I also have 2 relays covering HW and CH connecting to individual 2 port valves and firing the boiler when one or more valves are open. I was also considering adding another relay to control the boiler. If I added another relay for boiler control would Evohome then leave one of the valves open after switching the boiler off for a certain period so that the pump overrun provides heat elsewhere (is it CH or HW?) rather than just the bypass?

I'm clearly missing something but I don't understand how Top Brake's recommendation would work - wouldn't the heating also go on then when you just wanted the hot water as the CH valve is also latched open? Could someone provide a bit more of an explanation please?

[paulockenden]

I'm clearly missing something but I don't understand how Top Brake's recommendation would work - wouldn't the heating also go on then when you just wanted the hot water as the CH valve is also latched open? Could someone provide a bit more of an explanation please?

It relies on the fact that all of the HR92s will be closed, so no water will flow round the heating circuit.

P.

[morfsta]

It relies on the fact that all of the HR92s will be closed, so no water will flow round the heating circuit.

P.

Aha, that explains it. Thanks Paul.

The problem I have with that is the radiator on my airing cupboard has no TRV on it and I've also had to remove a HR92 off a towel radiator as it seems whoever fitted it originally put the valves on the wrong way around. The HR92 makes a loud banging noise on that one when operating, which interestingly the TRV never did..