Hot water heating time / amount

[sgreenwood1]

Hello.

I'm after some guidance if possible.

I have a gravity fed 117 litre hot water cylinder heated by a Worcester Bosch Greenstar 15ri boiler.

For years we've scheduled the hot water to come on for 45 mins in the morning and 45 mins in the evening. This provided enough water for washing up in the morning and evening and the occasional bath for the kids (all other items attached to the water are cold use only including shower). I can't recall ever running out of hot water.

A few weeks ago we ran out of hot water when the kids were in the bath so I 'boosted' it for 3 hours and noticed the boiler was running constantly for this time (no central heating was running).

I assumed perhaps it was a faulty tank 'stat so replaced it with a new Honeywell L641A1039 and set this to 60c.

After doing this I ran a hot water tap until it became cold and then switched the HW on. The boiler stopped heating the tank after 35-40 mins. I assumed, therefore, this was now a tank full of hot water and re-set the schedule back to 45 mins twice a day thinking this would ensure we always had a tank full when needed.

However, we're now still not getting enough hot water.

Today, right after the hot water had finished (again it clicked off approx 40mins) I ran the hot tap into the bath until it became cold. I estimate we got approx 70 litres of hot water in the bath (bath is 285L max capacity):

Is there an issue with the system? - perhaps a larger cylinder is required or modification to the schedule ? - or is it merely that we've 'never noticed' the issues until now, accept it and move on :0)?

Thanks in advance for your guidance.

 

[BlueLoo]

Perhaps the kids have just got bigger and need a deeper bath......

I have the same tank and it is more than enough to fill the bath with me in it to the overflow and i like a hot bath. (For reference). My stat is 2/3rds down and set at 60c like yours.

If that doesn't sound like it fits your scenario then maybe the boiler circuit needs attention. If you live in hard water areas, then the coil can become furred up stopping heat transfer.

 

[CBW]

Sounds like it could be scale as per @BlueLoo. However, let’s not rule out a failed motorised valve, or anything else. Do you have a 2 port or 3 port valve system?

 

[sgreenwood1]

Some further photos of what's installed.

3PV was installed c.5 years ago.

Pump within the last year - system was professionally flushed at the same time.

 

[CBW]

Try the following then:

• Wait until system has cooled down/cold
• Create a hot water only demand
• Carefully feel the pipes leading into the 3 port valve
• Carefully feel the pipe leading to the hot water cylinder coil

If both the last 2 points are similar temperature, eg hot, then I’d possibly be looking at scale

 

[sgreenwood1]

Try the following then:

• Wait until system has cooled down/cold
• Create a hot water only demand
• Carefully feel the pipes leading into the 3 port valve
• Carefully feel the pipe leading to the hot water cylinder coil

If both the last 2 points are similar temperature, eg hot, then I’d possibly be looking at scale

I'll do this tomorrow hopefully. Thank you.

If it points to scale what's the cure?

Would a system clean / flush (like what we had within the last 12 months) not remove scale?

The previous pump was replaced (at same time as flushing) because it had become 'bunged up' with black stuff and was noisy. You could insert a screwdriver into the pipes when it was removed and physically scrape the stuff out! The installer said to check the new pump showed '45' on the display when operating which it does.

 

[BlueLoo]

The scale will be on the outside of the internal tank coil. (ie in direct contact with the hot water).
So no plumbing flush will get near it as its the other side of the boundary.

If it is scale (who knows?) it will need a bit of effort to clean it out.....