Hot water help!

[Shellymc76]

Hi. I am new here and looking for some advice. In December I had a brand new Viessmann (13kW) heat only boiler fitted in the kitchen to replace a Glow Worm 30FF. I understand the Viessmann to have a bigger output than the old Glow Worm. My water tank is in an upstairs bedroom and is 22 years old. The CH seems to be ok but I am having teething troubles with the HW. It just doesn't seem to be as hot with the new boiler. I have messed around with the boiler temp. I currently have it on 5 (out of 6) which I believe to be around 70 degrees. I have the hot water cylinder set to 65 degrees. The HW comes on for one hour in the morning and two hours at tea time. I have two issues 1) The old boiler was set to a similar boiler temperature but the water cylinder was only set to 60. The timer settings were the same. Everything was fine and water was nice and hot. I have had to put the cylinder temp up to 65 with the new boiler to get it nice and hot. I can't understand why the new boiler is not performing as well as the old one. 2) This morning I had the HW on by itself for one hour and it was only luke warm. Can anyone offer any advice please? Thanks in advance.

Is the boiler a Vitodens 100?

What colour is the HW cylinder?

What size is your house, and how many radiators do you have? Are they all fully hot? Do they have TRVs? Are the radiator pipes the size of your finger, or the size of a pencil?

Have you got a pump
pumps

and a motorised valve
valves

visible, probably next to the cylinder? Some photos would help.

And of the cylinder stat
cyl stats

@Shellymc76

Hello?

@PigletJohn. Sorry for delay. Didn't get message until late last night and have been working all day.

Yes its a vitodens 100-W.
Cylinder is green.
3 bed semi (small)
7 rads. I think they have tvrs. They have white caps with +/- on.
Rads all hot.
Pipes the size of my finger.
Pump yes.
Motorised value - I think so. Diverter valve?
I have photos but can't figure out how to add them. No icon for attachments!

@PigletJohn aaahhh I've just ready that because I am a new member, I'm not allowed to post photos for a month! I can email them to you if you want to see them?

you can try using "message poster"

but I don't think it works for photos

If you can find a motorised valve, where is it? next to the cylinder?

does it have three pipes on it? one leading to the cylinder? Is that pipe hot?

A green cylinder is fairly modern, I would expect it to heat 120 litres of water in about an hour. It may work faster if you can set your timer/programmer to srt 30- 60 minutes before the heating comes on.

oh, and when the boiler is firing, look at the display. It probably has a "power" indicator, maybe three bars. Is it running at 5 bars? or less? It is normal for it to run at a higher setting at first when it's all cold, then to modulate down to lower power.

it may run lower when just heating the cylinder that when doing the rads.

Is the pump, or any other parts, new?

Do you know if the radiators were powerflushed before the boiler was fitted?

@PigletJohn yes valve is by the cylinder and three pipes come out of it. The one going to the cylinder is hot but not too hot to touch. No new parts for a while but the pump has been replaced twice i think in last 15 years. I dont think any powerflush was done prior to boiler installation.

I incresed the timer by 30 mins this morning and the water was better. I just cant get my head round why then old boiler was better/quicker at heating it.

Will have a look at the burner strength in the morning when water comes back on.

if for some reason flow is not good through the boiler or pipes, it will turn itself down (or off) if it reaches max temp, and this means that it will only run for short periods, thus reducing the amount of heat it can provide per hour.

If there is old sediment or rust particles in the water, they can accumulate into a restriction in flow.

But that's just a guess. Too early to say what the trouble might be.

Do you know if there is a system filter, such as a Magnaclean, which can trap circulating particles?

here are some of the popular ones (click for link)