Vaillant Turbomax 282e diaphragm

[Agile]

I have been reading all this for a bit of fun.

But I am surprised that no one mentioned what I have always done and thought was standard practice.

That is to start at zero HW flow and SLOWLY increase it until boiler turns on, then to stap and measure the flow rate and compare it with the maker's spec!

 

[Gasguru]

There are a few other boiler checks that need looking at including airflow..and unfortunately it's beyond diy.

 

[Johnking]

Hiya,

Sorry to resurrect this, I've still got the original problem.

I've replaced the diverter valve and micro switch, and set the switch to the most sensitive angle it allows.

I've replaced the heat plate.

I've added non-return valves to a mixer tap that was permitting back pressure onto the DHW pipe.

I've checked the stopcock to the mains supply and have 12l/m from both hot and cold taps next to the boiler.

I've added a 1bar booster pump to the DHW going into the shower and a non-return valve to the shower cold feed

But when I operate the shower (two floors up), it initially works but soon goes cold because the micro switch is not quite closing enough. If I slightly open a downstairs hot tap, that's enough to activate it and the shower runs hot.

What can I try next?

 

[Johntheo5]

As suggested somewhere above I think, open a downstairs hot tap very slowly until the boiler kicks in, then run this into a known container size until full while timing it, the minimum flow required can then be easily calculated. Have you another mixer somewhere?, the problem could be there even when turned off, is that downstairs hot tap supplying a mixer?.

 

[Justin Passing]

The restrictor was an original fit. Probably the type with a tiny rubber O ring. That will probably be well perished by now if it hasn't been replaced. It's supposed to restrict the max flow so you still get the specified temperature rise and flow rate as is in the spec.

Does the heat at the ch flow pipe actually go down the flow pipe while the HW is on?

As soon as you turn the tap off , the boiler will dump heat into the heating.


If you're feeling brave you could turn off the flow isolator valve while the hw is on. It should make no difference of course, but it might....
The snag is that t'll probably weep afterwards, though they usually stop after a couple of days.

There is a bypass valve. I don't know how it's connected and hence whether it could cause a problem on HW if it's letting by. Easy to check.

 

[Johntheo5]

The MIs say this boiler has a DHW flow switch setting of 2.7LPM and a minimum output of 11kw which means a dT of 58.4C or a DHW temperature of over 77C from (my) mains temp of 19C just now. Even though it shows a DHW temperature control I see only one temperature sensor, on the primary flow which apparently shuts the boiler down at 78.5C and has to be manually reset, since this is not happening then it still looks probably like the DHW flow isn't greater than 2.7LPM with the shower in service, for whatever reason?. If the boiler is switched off and the shower temperature control turned to max, the TMV should then only allow water flow from the boiler which can be easily measured.

 

[Johnking]

As suggested somewhere above I think, open a downstairs hot tap very slowly until the boiler kicks in, then run this into a known container size until full while timing it, the minimum flow required can then be easily calculated. Have you another mixer somewhere?, the problem could be there even when turned off, is that downstairs hot tap supplying a mixer?.

This (and sorry earlier person for not trying) has helped. The minimun flow at the boiler is 6.5l/m. In the upstairs shower I was getting about 5l/m with the thermostatic mixer at ful-hot, and the same at full-cold. BUT I tried it with the shower head off and I got the full 12l/m so swapped it with a different head and that's giving me 8l/m so I'm hopeful.

 

[Johnking]

The restrictor was an original fit. Probably the type with a tiny rubber O ring. That will probably be well perished by now if it hasn't been replaced. It's supposed to restrict the max flow so you still get the specified temperature rise and flow rate as is in the spec.

Does the heat at the ch flow pipe actually go down the flow pipe while the HW is on?

As soon as you turn the tap off , the boiler will dump heat into the heating.


If you're feeling brave you could turn off the flow isolator valve while the hw is on. It should make no difference of course, but it might....
The snag is that t'll probably weep afterwards, though they usually stop after a couple of days.

There is a bypass valve. I don't know how it's connected and hence whether it could cause a problem on HW if it's letting by. Easy to check.

This is a pic of the restrictor - there is a bit more plastic inside the fitting and it could easily go back (but note that this problem was happening prior to me removing it). The rubber part is actually fine.

Yes, the ch pipe does get hot.

By flow isolator, do you mean on the heating outlet pipe? Sounds risky maybe?

The bypass valve (30 on diagram) doesn't look like it would cause this problem does it?

 

[Johnking]

The MIs say this boiler has a DHW flow switch setting of 2.7LPM and a minimum output of 11kw which means a dT of 58.4C or a DHW temperature of over 77C from (my) mains temp of 19C just now. Even though it shows a DHW temperature control I see only one temperature sensor, on the primary flow which apparently shuts the boiler down at 78.5C and has to be manually reset, since this is not happening then it still looks probably like the DHW flow isn't greater than 2.7LPM with the shower in service, for whatever reason?. If the boiler is switched off and the shower temperature control turned to max, the TMV should then only allow water flow from the boiler which can be easily measured.

It certainly doesn't come on at 2.7l/m - see my other post today, it won't come on until about 6.5l/m.

I do notice that there's a lot of cycling, even when hot water is running next to the boiler, it turns the burners off and on, and the DHW temp fluctuates. Should that be happening?

 

[Johntheo5]

The boiler cycling on/off might be some temperature related protection but I only see one temperature sensor (on the primary circuit) mentioned, as stated avove, it trips the burner at 78.5C but has to be manually reset.

A boiler minimum output of 11kw with a DHW flow of 6.5LPM will give a dT of 23.5C and a HW temperature of 42.5C, (from mains at 19C) if the boiler doesn't modulate for one reason or other then a output of 28kw will give a dT of 61.7C and a HW temperature of 80.7C which means the primary water would be higher again and cause a trip but it shouldn't self reset except its from another sensor on the DHW outlet.

Does the DHW temperature from the hot tap feel "normal", Vaillant recomment that the DWW temp control is set to 6, 9 is max.

 

[Johntheo5]

Should also have said that a flowrate of 2.7LPM with the boiler at a minimum output 11kw will give a HW temperature of 77.4C, if mixed with (6.5-2.7) 3.8LPM of 19C will give a temperature of 43C so still possibly a mixing X over problem?.

 

[Johnking]

The boiler cycling on/off might be some temperature related protection but I only see one temperature sensor (on the primary circuit) mentioned, as stated avove, it trips the burner at 78.5C but has to be manually reset.

A boiler minimum output of 11kw with a DHW flow of 6.5LPM will give a dT of 23.5C and a HW temperature of 42.5C, (from mains at 19C) if the boiler doesn't modulate for one reason or other then a output of 28kw will give a dT of 61.7C and a HW temperature of 80.7C which means the primary water would be higher again and cause a trip but it shouldn't self reset except its from another sensor on the DHW outlet.

Does the DHW temperature from the hot tap feel "normal", Vaillant recomment that the DWW temp control is set to 6, 9 is max.

The over-temperature manual reset has never tripped. There is another temperature sensor (NTC) but it is behind the combustion chamber cover and I ain't touching that!

Water temperature on the hot tap is variable, it sometimes runs a bit cold and sometimes too hot.

So if this was working properly, should it just run the burner the whole time while it's delivering DHW? it's always cycled on and off

 

[Johnking]

Should also have said that a flowrate of 2.7LPM with the boiler at a minimum output 11kw will give a HW temperature of 77.4C, if mixed with (6.5-2.7) 3.8LPM of 19C will give a temperature of 43C so still possibly a mixing X over problem?.

I'm going to try a shower with the higher flow shower head.

 

[Johntheo5]

The over-temperature manual reset has never tripped. There is another temperature sensor (NTC) but it is behind the combustion chamber cover and I ain't touching that!

Water temperature on the hot tap is variable, it sometimes runs a bit cold and sometimes too hot.

So if this was working properly, should it just run the burner the whole time while it's delivering DHW? it's always cycled on and off

Yes, it should run continuously, but if the DHW flow coming from the boiler (at 11kw) is just above 2.7LPM then its temperature will be over 77C from mains at 19C so sailing fairly close to the wind under those conditions.
If you run a HW tap on its own do you get the same cycling and is that tap part of a single lever type mixing set or part of a two tap mixer or just a HW tap on its own?.

 

[Johnking]

Yes, it should run continuously, but if the DHW flow coming from the boiler (at 11kw) is just above 2.7LPM then its temperature will be over 77C from mains at 19C so sailing fairly close to the wind under those conditions.
If you run a HW tap on its own do you get the same cycling and is that tap part of a single lever type mixing set or part of a two tap mixer or just a HW tap on its own

Yes, I get the cycling. The tap (next to the boiler) is a two lever mixer and I noticed it was putting cold water back pressure on the DHW so I added a check valve to the DHW on the tap.