Oil Boiler Issues

Alfster

Hi guys,

Couple of issues I’m trying to rectify:

1) Optimising flow and return temps for hot water boost.
2) Hot water comes on intermittently by itself.

We have a one year old condensing Grant oil boiler in the cellar. For optimising flow and return temps I have purchased two pipe thermometers. I have the boiler temp thermostat dial about half way which is giving me 60 degrees flow and 48-50 return. Hot water cylinder is set to 55. With it being summer and therefore these values are only for a hot water boost seems a big drop? Is that good? Seems good but
looking through forums most people say 60/< 54 is ideal but will only achieve that with central heating on. 

2) We have a nest system. Hot water is off and heating is off all the time at the moment. Hot water  should only come on if it is boosted manually through the app. Hot water we only boost once in the evening which varies when we need it hence no schedule is set up. However, the boiler comes on randomly by itself to heat the hot water even though the nest is 100% off. Plumber checked zone valves and zone valve next to cylinder was faulty so was replaced. Still have the issue. Anyone had this problem?

thanks for any advice offered  

lohr500

I am no expert but 60 flow and 48/50 return sounds good to me when running hot water only. The boiler should be condensing with a 50 deg return.


Something definitely doesn't sound right with the wiring/pump/zone valves/Nest system if the boiler is kicking in intermittently even when the schedule is 100% off. We have a Hive system and in the summer we are using our Grant boiler just for hot water. It isn't kicking in at all outside of the scheduled hot water timings.

Our boiler is an external model and has a built in frost stat which fires up the boiler for a short period of time if the temperature inside the boiler housing falls to a dangerous level. I don't know if the internal versions have the same protection, but if they do, perhaps the frost stat is faulty?  

Assuming the replaced zone valve is OK, the other thing to check is to see if the circulation pump is running when the boiler randomly fires up. With hot water and central heating programmes set to off, the pump shouldn't be running. The only time the pump should be running is when either the tank thermostat or central heating room thermostat are calling for heat AND the control timer is set to an active time window for the hot water and/or central heating.

Does the Nest controller close to the boiler have any indicator lights on it? I don't know how the Nest system works, but with our Hive system, the boiler controller receives instructions from the smart thermostat wirelessly (or via a wired connection). There are two lights on the Hive boiler controller which illuminate when the controller is calling for central heating and hot water. If the Nest system is similar it would be worth checking to see if any lights are on when the boiler starts running intermittently.   

Alfster

lohr500 said:

I am no expert but 60 flow and 48/50 return sounds good to me when running hot water only. The boiler should be condensing with a 50 deg return.


Something definitely doesn't sound right with the wiring/pump/zone valves/Nest system if the boiler is kicking in intermittently even when the schedule is 100% off. We have a Hive system and in the summer we are using our Grant boiler just for hot water. It isn't kicking in at all outside of the scheduled hot water timings.

Our boiler is an external model and has a built in frost stat which fires up the boiler for a short period of time if the temperature inside the boiler housing falls to a dangerous level. I don't know if the internal versions have the same protection, but if they do, perhaps the frost stat is faulty?  

Assuming the replaced zone valve is OK, the other thing to check is to see if the circulation pump is running when the boiler randomly fires up. With hot water and central heating programmes set to off, the pump shouldn't be running. The only time the pump should be running is when either the tank thermostat or central heating room thermostat are calling for heat AND the control timer is set to an active time window for the hot water and/or central heating.

Does the Nest controller close to the boiler have any indicator lights on it? I don't know how the Nest system works, but with our Hive system, the boiler controller receives instructions from the smart thermostat wirelessly (or via a wired connection). There are two lights on the Hive boiler controller which illuminate when the controller is calling for central heating and hot water. If the Nest system is similar it would be worth checking to see if any lights are on when the boiler starts running intermittently.   

Thanks for such a detailed response. The circulation pump is definitely running. I took a video of it all when I caught it firing up by itself this evening. It’s hard to catch it as it does this random start up about once per day sometimes once every other day. I have attached a picture of the pump on during the intermittent start up. I didn’t check the nest module but will do next time I catch it on. There’s no issue with boosting. It always comes on when you ask for it but randomly comes on when you don’t so some days you are surprised by hot water you didn’t ask for 😂 

Reed_Richards

My oil boiler was a combi.  In order to provide a rapid supply of hot water it had a small internal tank which it kept hot.  This caused the boiler to come on seemingly at random.  Now the OP has a DHW cylinder so the boiler is probably not a combi but you never know.

Alfster

Reed_Richards said:

My oil boiler was a combi.  In order to provide a rapid supply of hot water it had a small internal tank which it kept hot.  This caused the boiler to come on seemingly at random.  Now the OP has a DHW cylinder so the boiler is probably not a combi but you never know.

Yes definitely not a combi boiler. 

Reed_Richards

Over-active use of a Legionella prevention feature that has not been turned off?

lohr500

It could be some form of legionella protection feature, but I've never heard of that on a domestic standard boiler set up.

The fact that the pump is powered up would suggest to me that either the Nest controller unit is faulty/not receiving the correct programme details, or the wider system hasn't been wired up correctly, or there is a fault with the boiler's integrated control panel.

I don't know much about the Nest thermostat system, but does it have a white Heat Link controller box located close to the boiler? If so, from what I can see on Google, it should have two indicator lights to show when the central heating and hot water circuits are energised.

If the hot water light is on when the intermittent fault occurs, that would suggest to me that there is a problem on the Nest side with either the programming or Nest controller/thermostat.

If no lights are on when the boiler fires up, then I suspect a wiring fault or a fault on the boiler's own control panel, since the boiler should not run unless it gets a "call for heat" signal from the Nest controller box on either the CH or Hot Water outputs. The "Call for heat" signal would be accompanied by the relevant indicator light on the Nest controller box.

Let us know what you see on the Nest Controller box, next time it happens and you can catch it!!!

Reed_Richards

Nest can do Legionella protection: https://support.google.com/googlenest/answer/9256656?hl=en-GB

lohr500

Nice one Reed_Richards. You may have solved the problem 👍 I wasn't aware that the Nest had that capability.

From the way Alfster describes using the system, perhaps the water isn't getting boosted for 2 consecutive hours in a 48 hour period. If his version of the Nest system has legionella protection, it could be kicking in.
From your link, if the thermostat shows a water droplet symbol in a white circle, then this shows the legionella function is active.

Alfster, can you see if that symbol is shown when the intermittent water heating kicks in?

If it is this, then the same link explains how to disable the function.

If this isn't the reason, then back to watching the control unit for light indications.

Alfster

Guys this is super useful thank you so much!!! I’m going to read through the nest link and try to catch boiler coming on so I can look at nest control panel. I will report back! Thanks again 

Alfster

Right. Great find Reed_Richards. My nest does have this and it is enabled! It says you should get an icon come up when this kicks in which I don’t get. One thing I always check when the boiler kicks in is that it is off in the app which it always is; I would expect it to show as being on in the app if it’s doing this. However, it maybe it appears on the main nest device which I haven’t checked yet. But if it is enabled and I definitely I am not using 2 hours of hot water in 48 hours then it should come on surely. I think next time I catch it on I also check the main nest device instead of the app for the legionnaires symbol as well as looking at the nest control panel by the boiler. If it is the legionnaires should I leave this enabled if it’s a safety feature and I’m not using the hot water much? It’s say legionnaires is killed at 60 degrees so is it a good idea to increase the cylinder temperate from 55 to 60? Thanks