Reducing Amount Hot Water - only been since the central heating has been on a lot

Hello,
Had a problem last year that has re-appeared again after the recent cold weather. Hot water is very hot at first, then after a short time (enough to fill a bath 1-2 inches) it rapidly cools. This only happens when the central heating has been running for long periods - like we've experienced in the last 2-3 weeks. This happened for a few weeks last year, but as soon as the weather improved and we reduced / stopped running the central heating the normal flow of hot water returned.

Anyone have any thoughts on what it could be?

Thanks,
Derrick

You do keep the Bm on 24/7
And your boiler on max?

Hi, apologies for hijacking your thread - but I am having a very similar experience and am looking for a bit of advice on what I should expect regarding hot water provision from one of these units.

Our house (standard modern 3 bed detached) has a BM2, fed by a conventional gas boiler (always at maximum), and no immersor. We have only lived in the house for a few months but I’m guessing the heating system was installed when it was built, around 10-12 years ago.

We had a baby this winter so the central heating has been on pretty much 24/7 and the store temp control dial is turned to the Winter setting. Everything on that front seems to work perfectly and the units always heat up really quickly when the rad thermostats click on. The issue is with hot water. When I turn on the tap or shower I get enough piping hot water to have a 10 min shower or half fill a bath before the water gets gradually cooler to the point of being look-warm. Is this normal performance or should I expect constant piping hot water with or without the central heating running?

I live in central Scotland, which is a soft water area, so I didn’t think scale would be an issue, but having read a few posts on this forum I am starting to wonder. Also, there is a bit of furring visible on the heat control valve and some corrosion around the outflow pipe on the lid of the BM.

I have no idea how well the previous occupants maintained the system but I have British Gas Homecare and have an engineer booked for our annual service/inspection next week and would like to be well armed with the relevant information/questions for him coming.

Thanks in advance,

Ross

First thing I would do is;
Drain some water out of the unit ( 2 buckets)
And check that the top tank on the unit or in the loft. The water level drop and the ball valve gives water.
Try that then reply.
Mike
MGC/H2O
Norfolk

Thanks Mike, I'll try giving that a bash.

Please excuse my ignorance, but how do I go about draining the unit as you suggest? Had a quick look but couldn't see anything obvious. I take it the water in the store is a separate system to the c/h, so it's not just a case of bleeding a couple of buckets' worth out the lowest rad? Sorry if this is a stupid question that's answered elsewhere on your site.

Cheers,

Ross

There should be a drain off on the unit at the bottom.
Or you can drain via a rad.
As the water in your unit is;
The boiler water
The heating water.
You really need to read the book.
If you have not got one
Down load one for free from Gledhill website.
You must establish whether unit is full of water / taking water when some taken out.
Then you can proceed further.
THIS IS NOT MY SITE BUT ANOTHER GUY CALLED MIKE.
Mike
MGC/H2O
Norfolk.

Cheers Mike, and apologies for the mistaken identity!

I had wondered if it was simply that the heating load was greater than the boiler output; so I turned of the c/h overnight but still this morning the shower ran look-warm after 10 min... so that doesn't seem to be the problem.

Thanks for the pointer to the Gledhill site, I have now downloaded the BM2 manual and will try draining a couple of gallons out the system tonight before checking whether the header tank in the loft is doing its thing. I'll let you know how I get on.

Ta,

Ross