Vaillant 630 bypass question

[Last Plumber]

Yes, only one day a week now.
They have to connect up an S plan (un-vented cylinder, regular condensing boiler, sealed system kit etc,), wire it up, then turn on test & commission it.
None of them have a clue about setting the by-pass which must reflect on what is going on in the real world.

Possibly.
I think a lot of people out there, pipe up, switch on and walk away.
I'm glad you're discussing it with them. People in your position play a vital role in putting things in the minds of those learning. Hopefully that makes them ponder over the subject matter and ask questions on. Especially if they ask questions on site and want to know 'why' something happens.
What percentage of your class would you say were genuinely interested in the work?

 

[Chuck]

Your description of what happens is okay until here:

The true minimum flow is therefore that required to produce the maximum permitted differential at minimum output. This means that you only need the bypass to operate when the boiler is cycling at minimum output because the heat requirement is less than the boiler output.

where you draw the wrong conclusion. During normal continuous operation the external bypass valve should not be passing flow. The regs haven't permitted 'always-on bypassing' for years because it wastes a lot of energy.

An external bypass circuit is not able (or intended) to dissipate 5kW continuously. It needs to have sufficient heat capacity to absorb heat from the HX at a rate of 20kW for the short period between when the zone valves all shut, which shuts down the burner, and when the heat exchanger has cooled sufficiently to avoid damage due to overheating the 'cold' section. This so-called 'over-run' time is typically 30 seconds or so because modern HXs have a relatively low heat capacity.

 

[chris watkins]

What percentage of your class would you say were genuinely interested in the work?

Almost all as I am not in an FE college & they are all apprentices.

 

[doitmyself]

During normal continuous operation the external bypass valve should not be passing flow. The regs haven't permitted 'always-on bypassing' for years because it wastes a lot of energy.

But I'm not talking about 'always-on bypassing', which wastes energy, but about the situation where the boiler is cycling on and off because the heat requirement is less than the boiler's minimum output.

An external bypass circuit is not able (or intended) to dissipate 5kW continuously. It needs to have sufficient heat capacity to absorb heat from the HX at a rate of 20kW for the short period between when the zone valves all shut, which shuts down the burner, and when the heat exchanger has cooled sufficiently to avoid damage due to overheating the 'cold' section.

You seem to be talking about the situation where the boiler is running flat out and it is suddenly turned off, e.g by the room stat or programmer. But if the burner has been turned off the boiler is no longer producing heat at 20kW. All you have is the residual heat in the pipes, which has to be dissipated somewhere. Do you really need a bypass capable of handling the maximum flow to do this?

 

[fishpond]

Low loss header is the way to go in my opinion

 

[Last Plumber]

Almost all as I am not in an FE college & they are all apprentices.

That's good then. What level are the ones at that you were discussing by-pass settings with? Would they be level 3? It's a long time since I was in college.

 

[chris watkins]

That's good then. What level are the ones at that you were discussing by-pass settings with? Would they be level 3? It's a long time since I was in college.

This is normally done right at the end of their Level 3 as it combines a lot of units they have done through-out (heating, wiring, Un-vented) it is kind of an end test & quite a challenge, how many of us could have wired an S plan aged 20 - 21 years?

I think a lot of people out there, pipe up, switch on and walk away.

I know so, not just from the fed back I get from them but because I go out regularly to thing like 2-3 year old new build flats with HIU, the pumps are set to fixed speed 3, none of the U/F heating coils have had the flow rates set. How much energy is being wasted for want of 10mins commissioning, after all it is a legal requirement.

People in your position play a vital role in putting things in the minds of those learning. Hopefully that makes them ponder over the subject matter and ask questions on.

With luck.
The longer I teach the more I come to think it is not the knowledge I can provide that is the important thing, it is the enquiring mind & the passion for what we do. Of course they have to trust you know what is what & they will find you out quick enough if you don't.

Especially if they ask questions on site and want to know 'why' something happens.

Are may favourite word 'WHY'
They get ask it so many times, don't just tell me the answer, tell me WHY.

 

[Frog67]

I contacted Vaillant support who advised me that the boiler does not require an external bypass as the built in one will (should) handle the excess heat/ flow when any external valves are closed.
I wont pretend to be an expert when it comes to setting bypass's but I'll certainly be paying close attention when (if) i get the install.

Chris Watkins, what a brilliant thing your doing with today's apprentices, i wish i had had that level of training when i was at college in 1986.

 

[chris watkins]

i wish i had had that level of training when i was at college in 1986.

So do I mate, if I had I wouldn't be stuck teaching the little buggers. Only joking.

It is not until we can look back that you can truly appreciate those who taught us for being good or bad.

Thanks for putting up with all my questions Ron H. AKA 28mm Ron (Dent Head)

 

[chris watkins]

I contacted Vaillant support who advised me that the boiler does not require an external bypass as the built in one will (should) handle the excess heat/ flow when any external valves are closed.
I wont pretend to be an expert when it comes to setting bypass's but I'll certainly be paying close attention when (if) i get the install.

I went right through the MI's & I couldn't see anything about fitting external by-pass being required.