Heating hot water only after solar thermal install.

[spacey3]

I had solar thermal installed recently, the system is a viessmann and goes with our viessmann boiler. The controls are on the boiler, seems to work well.

I spoke to viessmann technical after the install and they and the install advised to change the water heating from the boiler to only come on in the morning and evening when we would require it so that the solar could heat the water during the day.

I changed the timer to a mon-sun coming on at 0530 off at 0900 and again 1800 until 2200.

However the boiler now seems not to engage properly to heat the tank back up to 55 degrees.

On the control panel the cylinder prime pump is off when before it was on.

What setting in wrong?

 

[John.g]

Generally, like mine, the solar coil is mounted in the bottom of the cylinder with its sensor installed just above the top of this coil (called the solar store temperature) which starts/stops the solar circ pump on the differential temperature between the collector(s) top and this, on/off maybe 7C/3C. The top half of the cylinder normally 150 litres of a 300 litre cylinder etc only heats this and has the cylinder stat located just above the boiler coil return.
In the summer the solar coil will heat the whole tank fully or the bottom half if the cylinder SP is higher than this temp.
Some solar controllers also have the option to stop using the boiler coil even if programmed on if the solar circ pump is in operation.

What is the DHW circ pump which is just now showing on?.

 

[spacey3]

In answer to your question I am not sure.

All I know is that previously before the solar install everything in the boiler control was set to automatic, so the water would come on just before the heating would and it would reheat throughout the day when it dropped below a certain temperature.

It's a Vitodens 200 boiler (B2HA model) which my understanding is 4 pipe as opposed to most boilers being 2 pipe. So there is a pump circuit or something inside the boiler that diverts the water to heat the coil in the cylinder and the water.

I assume the DHW Prim pump is the circulating pump to do this. Though I am not sure what circ pump is.

After the Solar systems where installed (the solar is a 300 3m2 panel set with an SM1A controller that links to the boiler so no need for any separate controls).

I was advised to change the heating to just the morning when required and the late evening when required.

This is when the hot water didn't fire up during those two times the same.

I took the images of the control this morning for you - the cylinder temp on the top sensor was 48c and the solar one was 23c

My water temp is set to 55c.

The system had been on for around 22min, the DHW circ pump was on but the prim pump was off.

 

[John.g]

Wouldn't pretend to know anything really about this system but what seems to be going on is a form DHW temperature suppression (lower hot water temperatures in effect than the setpoint temperature), Don't know why this is going on, you just timed your DHW heating to come on for two periods, morning and evening and there would be little or no solar generation during these two periods at any rate.

Will have a read of the system but it does seem highly complicated, presume you have a 300 Litre cylinder with two heating coils.??.

 

[spacey3]

Yes I did as this is what I was advised to do. Originally it was set to auto, which means it mirrors the heating circuit.

Yes I have a joule twin coil horizontal cylinder in the loft.

It has the solar collect temp sensor in the bottom, the hot water one is in the middle.

I will put it back to auto to see if it does anything differently.

I know I have a km-bus

 

[spacey3]

I managed to figure out a setting in solar under control 2 was set to only 50 degrees for the temp of the solar. I increased this to match the 55 set on the boiler.

I also changed the setting to be automatic on the boiler for the DHW to match heating. This meant the the water was being heated up in the morning and reheated in the evening also.

However, it seems it is still only heating to 50 degrees instead of the setting of 55.

What is preventing it from reaching 55?

 

[John.g]

Have you a link to where you are reading these parameters from?.

 

[spacey3]

The instructions that came with the module attached to the pump are these - page 14 08 reads Maximum cylinder temperature which is set to 60, but then page 15 which I adjusted also reads - 11 Set DHW temperature, solar from factory was set to 50 but I changed to 55 to match the boiler.

As I said previously I noticed that when you corrected me and I reset the boiler to be DHW and Heating to auto as opposed to separated times it is reheating when it gets very low.

I also now have VI connect which allows me to see most things on the phone.

 

[John.g]

Set the boiler to 60C and page 14 08 to 55C and 15 11 to 55C, the controller seems to average these last two parameters for a certain length of time anyway, the boiler SP should always be at least +5C higher than the cylinder SP.