Heat Bank Problems

Pat01

New Member
Hi, Hope you guys can help me out.

Two problems:

My system:
Pandora Heat Bank which does the DHW. Its max temp is set at 75c and minimum at 65c. The DHW from the Heat Bank is set to on from 6am to 12pm and 3pm to 9pm. the Grundfoss pump on the return at the Heat Bank is set at speed 2.

I have a Vaillant 637 System boiler that does the CH. The pressure in the boiler is set at just over 1 bar and the stat on the boiler is set to its maximum (75c).

Problem 1.
The CH stays on for most of the day (at present) and is controlled by a Danfoss Stat set at 20c, as a result I have noticed the Heat Bank is extremely slow in warming up. The first person to use the shower normally at around 8am gets good heat however the second user even after 1 hour gets at best warm to luke-warm water. I have noticed the temp on the Heat bank after the second shower to be as low as 45c. On average I have recorded that the Heat Bank takes 1 hour to get from 45c to 55c. What could be the problem? Any help would be appreciated. To help - during the Summer when the CH was off - I did not notice any problems and we seemed to get piping hot water consistently!

Problem 2.
The Vaillant 637 boiler (37kw) runs 16 rads over 3 zones split equally) I do however notice a lot of cycling - can anyone help me resolve this issue.

To all thanks in advance for your help.

Pat
 
Pat, on the HW side; The incoming water supply can be very low in temperature this Winter & will use more energy from your heat bank to heat it. So increase the boiler thermostat until the weather gets milder.

As for you central heating, again it's all about current temperature.....Simples.

One thing that would be worth checking though; Is your DHW stainless steel HX a bit blocked up?? That can have a big effect, as it reduces the heat transfer area between Primary & Secondary water.

Heat banks are not popular in the trade as they sludge up after time, though yours may be an indirect one. Regardless, your system will need cleaned regularly with any kind of head bank.
 
Dick, how can they increase the boiler thermostat when they have said "and the stat on the boiler is set to its maximum (75c)"?

BB
 
To help - during the Summer when the CH was off - I did not notice any problems and we seemed to get piping hot water consistently!

There's your problem!
CH has priority flow.

Either Re-wire or Re-pipe to give HW priority!
 
hi,

I just ran a a test where only the DHW was on, but it still took an hr for the temp of the heat bank to rise 10c from 45c to 55c!!!
 
Good point BB, but the dial doesn't have setting on it.

Great wee boiler that, but we have found the internal by-pass is mid-setting & the boiler can short cycle.
 
Consider careful timing of when the central heating and DHW heating come on. Depending on the valve system 2 2-wy or 1 3-way)and priority, it is possible that if they both come on at the same time, the boiler will struggle to cope and the heatbank will actual heat the water flowing through it instead of being heated by it. This will cool the heat bank.

May be give the heat bank a half hour blast of heat before the CH starts and then come on again when the CH has been going for an hour or two and the temp is back up.



AFAIK Valiant boilers can be adjusted to give a flow of above 75c. It is not in the user handbook but the tech guys at valiant know how to program it.
 
"Great wee boiler that, but we have found the internal by-pass is mid-setting & the boiler can short cycle."

Is there a way to overcome this as this is a really annoying problem with the 637, even though it claims to have an anti-cycling economiser.
 
It's probably sludged up with gunk and scale.
These things sludge up for a past time.

Soloution = Rip it out and fit an unvented cylinder.
 
Sounds like another ridiculously overspecced boiler!

What size pipes do you have between the boiler and the heatbank? 28mm minium for anything over 24kW.

Does the boiler show S.53 on the status codes when it is turning itself off? If so you have to wait for 8 minutes or so before it relights.

I would try range rating the boiler doen to 20kW using D.0 on the control panel and seeing what happens ;)
 
Razor,
The pipes between heatbank and boiler are 22mm. I have read about range rating but the Valliant manual says its self rating ie starts at the max rate but then automatically rates itself down to the required level. Is it still worth doing??

I get your point about a ridiculously over-sized boiler and I regret buying it now. But at the time these plumbing suppliers always push you to buy the biggest and most expensive!!!!

thanks...Pat

Should have come on here in the first place.

Anyway, someone also suggested ripping the heatbank out and putting in an unvented cylinder but isn't that what a Heatbank is??
 
Is there a way to overcome this as this is a really annoying problem with the 637, even though it claims to have an anti-cycling economiser............Yes, any good RGI should be able to adjust the by-pass & anything else!! I tend to agree with others, could be oversized & modulating down, waiting, back on again & so on!!
 
Hi Dick,

What exactly should I ask the RGI to do?
Don't want to look like a prat? you know what I mean!

thanks
 
Try to get one that specializes in Valliant, tell him you think it's cutting off too soon & not heating your heat bank as a result. Also, get him to check if for any reason, you're not getting good stratification in your heat bank.
 
Dick,

Thanks will do. I've also got the Heat Bank people coming over on Tuesday to have a look, anything in particular I should ask them to look at on their side.
 
DPS are a good suppliers & their technical guys are highly respected. I would put money on you just having commissioning problems & adjustments need to be made.
 
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