Evohome and oil boiler questions
Discussion
I've got a Worcester Danesmoor 15/19 oil boiler. It's a low-level flue room-sealed system boiler, built in 2003. It has an expansion vessel, onboard pump, and thermostat, but not the optional programmer. The boiler provides heating only, not hot water, so there is no diverter valve. The boiler is installed in the attached garage. There are 11 radiators (4 bed dormer bungalow).
When I moved in 6 years ago, the heating was controlled by a Danfoss 5/2 day electronic programmer, wall-mounted in the hallway, and all the radiators had Danfoss TRVs. Everything worked fine, but I got through a fair amount of oil, heating some of the rooms when they were unoccupied. I decided to fit an Evohome system - controller and relay box, and 9 HR92s (2 of the rads are just left with the TRVs turned down to the frost setting).
When the boiler was installed, the live supply was simply switched by the battery-operated remote programmer, so when the programmer switches the system off, there is no power at all to the boiler. This means that everything just stops dead - pump, burner, and fan all switch off. Looking at the wiring diagram, the optional Worcester programmer (not fitted from new) seems to be able to control the pump and burner separately. This seems sensible to me, keeping the water circulating after the burner has switched off. The way it was originally installed, this obviously has never been happening.
However, the way the external programmer and TRVs worked together meant that the boiler was running pretty much constantly for several hours, with the burner switching on and off under the control of the boiler's water thermostat. The pump tended to "run on" when the burner was off. The thermostat in the programmer rarely shut down the boiler, as the hallway was generally too cold.
I fitted the Evohome kit yesterday, wiring the relay box in the same way as the original external programmer - switching the live supply to the boiler. Everything works, but I'm not sure if it's good for the boiler. It is cycling a lot more than it used to once the HR92s are up to temperature, completely switching off for a few minutes. I wonder if this is potentially damaging the boiler, stopping the pump when the burner box and heat exchanger are hot?
I've increased the minimum cycle time to 5 minutes. Should I decrease the maximum cycles per hour too?
Would it be advantageous to fit some kind of pump run-on timer? If so, what and how? The wiring panel in the boiler has the facility to wire the pump separately, but there is no controller, just a wire link.
Would it be a good idea (or even possible) to put the Evohome controller in the hallway, and set the hallway zone to use the controller's sensor rather than the HR92's sensor? Could I set the HR92 to 18 degrees, with the controller set to 22 degrees (basically what I did with the old TRV and programmer)?
Maybe I'd have to refit the old wax TRV head to the hallway radiator, so the zone never reached the set temperature?
I've no idea if there's a bypass valve fitted, which the boiler installation manual says is required if all the radiators have TRVs.
Am I worrying unnecessarily?
When I moved in 6 years ago, the heating was controlled by a Danfoss 5/2 day electronic programmer, wall-mounted in the hallway, and all the radiators had Danfoss TRVs. Everything worked fine, but I got through a fair amount of oil, heating some of the rooms when they were unoccupied. I decided to fit an Evohome system - controller and relay box, and 9 HR92s (2 of the rads are just left with the TRVs turned down to the frost setting).
When the boiler was installed, the live supply was simply switched by the battery-operated remote programmer, so when the programmer switches the system off, there is no power at all to the boiler. This means that everything just stops dead - pump, burner, and fan all switch off. Looking at the wiring diagram, the optional Worcester programmer (not fitted from new) seems to be able to control the pump and burner separately. This seems sensible to me, keeping the water circulating after the burner has switched off. The way it was originally installed, this obviously has never been happening.
However, the way the external programmer and TRVs worked together meant that the boiler was running pretty much constantly for several hours, with the burner switching on and off under the control of the boiler's water thermostat. The pump tended to "run on" when the burner was off. The thermostat in the programmer rarely shut down the boiler, as the hallway was generally too cold.
I fitted the Evohome kit yesterday, wiring the relay box in the same way as the original external programmer - switching the live supply to the boiler. Everything works, but I'm not sure if it's good for the boiler. It is cycling a lot more than it used to once the HR92s are up to temperature, completely switching off for a few minutes. I wonder if this is potentially damaging the boiler, stopping the pump when the burner box and heat exchanger are hot?
I've increased the minimum cycle time to 5 minutes. Should I decrease the maximum cycles per hour too?
Would it be advantageous to fit some kind of pump run-on timer? If so, what and how? The wiring panel in the boiler has the facility to wire the pump separately, but there is no controller, just a wire link.
Would it be a good idea (or even possible) to put the Evohome controller in the hallway, and set the hallway zone to use the controller's sensor rather than the HR92's sensor? Could I set the HR92 to 18 degrees, with the controller set to 22 degrees (basically what I did with the old TRV and programmer)?
Maybe I'd have to refit the old wax TRV head to the hallway radiator, so the zone never reached the set temperature?
I've no idea if there's a bypass valve fitted, which the boiler installation manual says is required if all the radiators have TRVs.
Am I worrying unnecessarily?
The main stat is probably doing TPI so it cycles the boiler on and off with the on cycles getting shorter as it gets closer to the set point. The idea being it won't overshoot, and then keeps topping up the heating to stop it dropping too far the other way.
There should be a cycles per hour setting, 3 6 9 12.
Not sure how that all hangs together with the individual trvs though..
There should be a cycles per hour setting, 3 6 9 12.
Not sure how that all hangs together with the individual trvs though..
We have the same sort of setup and when I asked the guy who fitted the boiler about turning it on/off he said just give it power when you want it and turn power off when you don't want it, so I think it's fine how you have it.
You should have a bypass though. Or just put a manual valve on one rad and leave it open.
You can set the max no. of cycles on the Evohome.
You should have a bypass though. Or just put a manual valve on one rad and leave it open.
You can set the max no. of cycles on the Evohome.
Good to know that the boiler doesn't need a pump run-on timer.
I can't see an automatic bypass valve anywhere. Since I've lived here, all the radiators have had TRVs fitted. I just left the TRV in the kitchen/diner fully open. It's the furthest rad from the boiler, and the last one to warm up. With the TRV fully open, it never got too hot in the room.
My original idea with the Evohome system was to leave the manual (fully open) TRV fitted in the kitchen/diner, put the Evotouch controller in there, and use it's on-board sensor to control the kitchen/diner zone purely by switching the boiler on and off. The supplier told me that this wouldn't work, I needed to use an HR92.
I can see where they were coming from. Without an HR92, the zone would overshoot. Not a problem for me, as that's what it did before, never got too hot.
I've just removed the HR92, and it seems to work OK, boiler firing when the controller sensor calls for heat.
It does look like I'll need to keep the HR92 bound to the zone though, as a device has to be declared in the configuration.
I can't see an automatic bypass valve anywhere. Since I've lived here, all the radiators have had TRVs fitted. I just left the TRV in the kitchen/diner fully open. It's the furthest rad from the boiler, and the last one to warm up. With the TRV fully open, it never got too hot in the room.
My original idea with the Evohome system was to leave the manual (fully open) TRV fitted in the kitchen/diner, put the Evotouch controller in there, and use it's on-board sensor to control the kitchen/diner zone purely by switching the boiler on and off. The supplier told me that this wouldn't work, I needed to use an HR92.
I can see where they were coming from. Without an HR92, the zone would overshoot. Not a problem for me, as that's what it did before, never got too hot.
I've just removed the HR92, and it seems to work OK, boiler firing when the controller sensor calls for heat.
It does look like I'll need to keep the HR92 bound to the zone though, as a device has to be declared in the configuration.
I've been playing around with this for a few days. I'll post my findings incase it will help anyone else in the future.
Although the Evohome controller has a sensor built in, it isn't capable of controlling a zone on it's own - unless the system is set up as a basic thermostat and boiler relay (whole-house setup).
As soon as you start adding zones with Evohome radiator valves or other add-ons, each zone needs to have a device bound and on line, although the controller doesn't check that it's actually fitted.
In my case, to create the kitchen diner zone, I had to bind an HR92, but not actually fit it. It needs to be on line, or the boiler will not fire. If I take the batteries out of the HR92, the boiler won't fire, even though the controller's internal sensor is calling for heat to the zone.
I'm planning on getting an unvented hot water cylinder. At the same time, I'll get an ABV installed, and refit the HR92.
Although the Evohome controller has a sensor built in, it isn't capable of controlling a zone on it's own - unless the system is set up as a basic thermostat and boiler relay (whole-house setup).
As soon as you start adding zones with Evohome radiator valves or other add-ons, each zone needs to have a device bound and on line, although the controller doesn't check that it's actually fitted.
In my case, to create the kitchen diner zone, I had to bind an HR92, but not actually fit it. It needs to be on line, or the boiler will not fire. If I take the batteries out of the HR92, the boiler won't fire, even though the controller's internal sensor is calling for heat to the zone.
I'm planning on getting an unvented hot water cylinder. At the same time, I'll get an ABV installed, and refit the HR92.
Whilst we have a bypass, the towel rails in the bathrooms are basically treated as bypasses too, they're on manual valves and I've set it all up so that they will always come on if the boiler is on, be that for hot water or a single radiator somewhere, my theory being, they don't really waste much heat, and it's always good to heat bathrooms/towels so that they dry.
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