System boilers - hot water tanks, separate flow temperature possible

[ant2]

I have a vailant ecotek plus 438. 20 radiators and an UFH system. House built in 1990 and back extended recently.
Cavity wall insulation, ceiling insulation and insulation between most internal rooms.
100mm-250mm loft insulation.
4 zone valves.

I would like to reduce the flow temperatures of the system boiler from 62c to atleast 50c or maybe lower for the
Ch, we have oversized radiators.
The issue is I need to heat HW and this needs to hearlt to 60c at the tank atleast once per week To kill the bacteria.

There is a HW flow temperature dial but it doesn't get used and I read this is the idea for system boilers.

Is there any way to wire/control these boilers to increase the flow for HW calls?

 

[ianmcd]

Not with that boiler no, but what you can do if you have an immersion is fit a programmable timer on the immersion and set the immersion thermostat to 60 and set the timer to come on once a week for 1 hour, you can then lower the boiler set temp

 

[ant2]

Not with that boiler no, but what you can do if you have an immersion is fit a programmable timer on the immersion and set the immersion thermostat to 60 and set the timer to come on once a week for 1 hour, you can then lower the boiler set temp

That's a good idea..

unfortunately for me the plumber fitted a shallow immersion inside the hw tank and it only heats the top of the tank and the bottom stays luke warm.
I bought a new one and have it next to the tank, never fitting it as Id have to remove the whole tank or take the ceiling down to fit it.
I may experiment again though and look at fitting a timer Switch If I can get it hot enough. Thanks

 

[JonathanM]

Is yours definitely a system boiler? I read the 438 was a regular open vent boiler.

 

[ianmcd]

I have a site with similar problems that when built, the plasterboard was already all fitted then the HW cylinders installed , there is not enough headroom to replace the top entry immersion elements so we core cut a hole about 125mm directly above the element and keep the bit we have cut, remove the element install the new one, and brace above the hole then put the cut out back in and screw it in place, they are all inside a cupboard so cant be seen really

 

[ianmcd]

Is yours definitely a system boiler? I read the 438 was a regular open vent boiler.

438 can be fitted open vent or sealed system

 

[JonathanM]

438 can be fitted open vent or sealed system

Just noticed in the user manual it says you can fit optional accessories to set the hot water temperature. Might that make it work?

 

[JonathanM]

Also, I remember now reading this in another forum when I was looking into PDHW.

"Vaillants systems will use HW priority when using their controls & wiring centres. You don't just need the GreenIQ 4 pipe boiler to do it. Any other their heat & system boilers will do it when using the Wiring centre and Vaillants control. You can either use a diverter or 2 two port valves, and I like to use the Probe on the tank too (VR10 I think). You can set DHW temp then, along with DHW flow temp (For reheat) and maximum time spent reheating DHW."

EDIT: But I think that post is more recent than the OP's boiler.

 

[ant2]

Thanks all. Buying vailant wiring centers and controls seems a bit ott for me.

I think the immersion once a week to kill the bugs is the best route. I have just been putting off replacing it with the 36" one as I have no doubt the plumber, who had no idea what he was doing probably got loads of mastic over the gasket and threads of the immersion. Meaning I worry about removing it without damaging the tank, leaking afterwards and or the drain off not working / leaking after and all those things that seem to happen.

 

[ianmcd]

leaking afterwards and or the drain off not working

no need to drain the cylinder to swap a top entry immersion just turn off the isolator valve and open the hot taps

 

[fixitflav]

438 can be fitted open vent or sealed system

But is it system or heat-only?

 

[oldbuffer]

Heat only.

 

[ant2]

no need to drain the cylinder to swap a top entry immersion just turn off the isolator valve and open the hot taps

I was wondering about that as every single guide and YouTube video I watched stated it had to partially drained via the bottom drain hose. I suppose it depends how low all the tap feeds are.

I may buy one of those box spanners, wd40 it the night before and just see if mine undoes easily as it's only been on 4 years.. if that plumber has covered it in compound and it doesn't move, I'll just leave it.

I see plumbers suggesting putting a jointing compound all over the new fibre washer, this seems counter productive as fibre washers are great for sealing leaks
And if the compound goes hard, it's not easy to remove without damaging the tank.
then ptfe all over the thread... which seems like a bad idea because the thread and soldered boss are so fragile and this could cause over tightening of the thread.

Wouldn't it best just to put a bit of lsx over the immersion threads and screw it so the washer is tight to the tank by hand?
Then it's easily removed and shouldn't leak.