Red compact 18 boiler

craig3940 wrote: »

Hello,

Bought this boiler in May and it has worked fine throughout the summer months in summer mode (just for hot water).
Changed it to winter mode yesterday but having an issue and I hope someone can help.
I have a Salus rt510tx thermostat and it is sending for the boiler to turn on. The only way the boiler will turn on is if the timer (on the boiler) is due to be on. Does that mean I need both the timer on the thermostat and timer on the boiler to be on at the same time always or is there a way just to run it off the one?

The timer on the boiler simply allows the boiler to operate. If the timer is on AND the thermostat says it is too cold then the boiler will fire until either the thermostat is satisfied (reaches its set temperature) or the boiler timer switches off.

In your case your thermostat is programmable which means that it also has its own timer specifically for the heating, so to provide central heating the boiler will have to be ON, the timer on the thermostat will also have to be ON, and the room temperature will have to be lower than the the temperature set on the thermostat.

craig3940 wrote: »

Also when the boiler is operating, it sends all the heat primarily to the hot water tank. So I don't get any heat to my radiators for maybe 2 hours (when the hot water has reached its desired temperature). Now in the summer we heated the hot water for 1.5 hours in the evening and this was sufficient until the next evening, but now in the morning it is heating it up again a few degrees (maybe from 50 to 60) which is not necessary. I jump into the shower or run a tap, and again the rotary switch shuts off the heat to the radiators (so the temperature drops in the rooms) and directs it to the water tank again (which i don't want). Any help please will be greatly appreciated.
Thank you.

The hot water will usually be controlled by a thermostat on the hot water tank. If the temperature drops (you use hot water) this will tell the boiler to fire and heat the water tank back up to temperature.

Depending on your central heating layout the boiler output could be "shared"in a number of ways via gravity or control valves which we would need to know more about before we are certain what is happening.

Also, if you have a timer for your heating does it have a separate timer or control for water? if so, you would be able to turn this off while heating to stop the boiler output being diverted or shared with the hot water tank.

Another issue however is that you may have a "thermal store" rather than a hot water tank. If this is the case then your hot water will be heated regardless whenever your heating is on and things get a bit more complicated.

From a quick look at the manual it seems that the boiler can produce instant hot water (like a combi boiler) or can be used to fill a hot water tank to a temperature set by an external temperature sensor directly measuring the hot water storage tank.

There are then 2 options for how the boiler measures the hot water tank, a thermostat (on/off) or an NTC thermistor.

If you can see the temperature of the hot water tank on the boiler screen then you will have the NTC thermistior option fitted.

If this is the case (which it sounds like) then you should set the "Set tank temp" to the temperature you like your hot water, and you should set the "set water temp" (the temperature of the water coming out of the boiler) either to maximum, or to a temperature at least 10 degrees higher than the desired tank temperature setting.

If these two temperature settings are too close together the water coming out of the boiler may never be able to heat the tank enough to reach the tank temperature and the boiler will run for a very long time (or possibly forever) trying to heat the tank to your desired temperature, and while this is happening it will be diverting precious boiler output away from your central heating!

Happy to help, glad the info is coming in useful.

The "water temp" is the heat of the water in the pipe just before it leaves the boiler. As there is only a small amount of water in that pipe it will cool down much quicker when the boiler switches off compared to the big insulated tank of domestic hot water (DHW) wherever that may be located.

Think of the water temp as the temperature of the water coming out of your bath tap and the DHW as the temperature of the water already in the bath.

If you want to get your bath from 55C to 60C using tap water at 61C it will take loads of water (and therefore time) to get the bath up to 60C. However if the tap water was at 80C you would raise the temperature using much less water (and therefore in much less time). When the tank (Or bath in this example) reached 60C, the boiler will turn off the water to the tank and is therefore able to dedicate its efforts to your heating.... providing the thermostat is asking for heating. If not, the boiler will switch off until needed again.

In your example the boiler was at 60C and the tank required temperature was also set to 60C. The water may lose a degree or two on its way to the tank so it could arrive at say 58C. This means that you would eventually get your 45C hot water tank up to 58C, but it will never reach the 60C required temperature so will never stop asking for more heat and so will never switch off the boiler until the 1.5 hour timer you set turns off and overrides it.

Personally, I would set the boiler output water temperature temperature as high as it will go. The only reason to turn it down would be to prevent any temperature overshoot in the tank due to the response time of the PTC thermistor. Having the water temperature on full will also minimise "short cycling" of the boiler which is better for the boiler and for its efficiency.

What you will hopefully see tonight is that with your higher boiler output temperature set to 70C (or maximum which is usually about 82-85C) is that your "water temperature" should quickly rise from 24 to say 70-85C and stay there. This water will then fill your (currently) 45C DHW tank and this temperature should slowly begin to rise as the 70-80C water mixes with the 45C water already in the water tank.

Then when the DHW tank temperature finally hits 60C your boiler should then shut off all by itself (even if the 1.5 hour timer is still "on") because the boiler will identify that the DHW has reached your desired temperature..... and you're done!

Hi again.

Glad things are improving!

Yes it is easy to reduce the temperature to 30-40 before the hot water is diverted, just set the DHW temperature from 60 down to 30 or 40, however the issue will then be that the boiler will only ever heat the water to 30 or 40 degrees which could be a problem as this would be the maximum temperature which will come out of your taps. This would however provide the improvements you suggested of safety for youngsters and a faster heat up time. You could possibly run the DHW tank back up to say 60-70 once in a while to kill off anything which may be slowly breeding in there!

If your hot water has a separate timer, or on/off switch for the hot water you can just turn the hot water off while you are using the heating, or set the hot water timer to come on, say an hour before your need your heating to come on so the water is already fully up to temperature before the heating is needed?

Auto eco mode is used when the boiler has to start and stop a lot, this keeps the boiler in a "low power idle" state for 10 minutes in case it is needed again quickly and if it isn't needed after that it shuts down fully.

This is more efficient than turning on and fully off at regular intervals as it keeps the flue warm and ensures a clean and efficient burn straight away.

craig3940 wrote: »

Yes your suggestion to reduce the dhw down to say 30c seems the only plausible way to bi-pass heating the hot water when not needed. We have no separate timer for hot water unfortunately.
Last couple of questions (sorry -I'm so unknowledgeable on these kind of things).

Thanks once more.

No problem at all, heating systems are a bit of a fascinating obsession with me. I think I should have been a plumber! :rotfl:

craig3940 wrote: »

1. What does 'pump turn on' mean exactly mean? It is set at 50c.

1: I believe that the pump turn on only runs the pump when the boiler reaches a certain internal temperature, otherwise it would end up pushing cold water into the how water tank coil and removing hot water which is the opposite of what you want

craig3940 wrote: »

2. With the 3 point valve (notary) - is it always fully open or fully closed? Is it never half open to heat partially the hot water and heating at same time?

2: If this is a "3 Port Valve" (Often referred to as a mid position valve) it will send water to either the central heating or water tank (depending on what is being requested by the thermostats), however if both are calling for heat the valve sits in the middle position and allows water to be shared between both circuits.

If you can find yours you can see what position it is in by looking at the slider on the side. It will look something like this:


What needs to be considered with a mid-position valve arrangement is that the hot water coil is usually much easier to push water through than all the radiators. This means that the majority of the hot water flow from your boiler would try and flow via the "easier" hot water circuit.

For this reason the system will usually need to be "balanced" by the use of a gate valve in line with the hot water coil. This is used to artificially increase the resistance of the DHW coil to water flow so that it matches the resistance of the radiators. This ensures that when the valve is in the middle position the amount of water flowing to each side of the system is roughly equal.

If you notice a huge drop in central heating output whenever both the central heating thermostat is on AND the DHW tank is colder than your set point then it could also be that this gate valve is fully open (or non-existent)!