Boiler schematic explanation

[ChrisR]

The problem comes about when the hot water is turned off.
The diverter valve closes and the hot system water in the plate heat exchanger is sat there chucking all its heat into the domestic side of the Plate Heat Exchanger. This causes the domestic water to get rather hotter than it should be and a PHE full of overheated domestic water will be in the pipework if the tap is re-opened before the PHE cools down.

A giannoni diverter valve closes the diverter section when the tap goes off and takes the pump out of circuit from the PHE.
Simply leaving it running during the CH anti cycle time cannot clear this hot system water from the PHE

That doesn't sound right to me. The blue text - when the diverter closes, it's closed to the PHE. The open route is through the CH circuit.
So when the tap's turned off, the boiler water in the PHE just sits there. All of its heat would go into the DHW that's sitting in there, so that would heat up a bit more, but then it would be cooling down with time.

So after a CH period, overrun or no overrun, there shouldn't be any hot primary water in the PHE, unless as I suggested way back, the diverter is "letting by". In that case the stationary tap water sitting in the PHE would get up to the 80 odd of the CH water. So when the tap's opened, you get scalded.

The red text - other way round you might say - the PHE is taken out of the live pump circuit. The pump circuit carries on - through the CH.

Getting another pic together....

One of the green pipes comes from the Diverter (Orangey). I think it's the one on the left, the lighter one.
If the hot tap hasn't been used for a while, that pipe, and the whole of the DHW heat exchanger, should be COOL.

I bet it isn't, because the DV is letting water through, because of dirt in the system.

 

[Slugbabydotcom]

That doesn't sound right to me. The blue text - when the diverter closes, it's closed to the PHE. The open route is through the CH circuit.
So when the tap's turned off, the boiler water in the PHE just sits there. All of its heat would go into the DHW that's sitting in there, so that would heat up a bit more, but then it would be cooling down with time.

Precisely so what I am saying is that if the tap is quickly re-opened then the overheated water in the PHE will be straight out of the hot tap. This is the problem that I understood was happening

We do seem to be saying the same thing in our own different ways.

To go what is hopefully the last leg we need to clarify the exact problem

To sum it up lets say that:-

If the problem occurs when you first turn the hot tap on after having the system at full temp then Chris is right and the diverter valve is letting by.

If the problem occurs after the first time and at any time you re-open the tap without allowing the PHE to cool down then it is down to the common fault that I am saying they have now addressed.

 

[Nige F]

Geez, is being Corgi registered a secret society?

)?

many a true word spoken in jest

 

[DP]

It has nothing to do with secret society, more to do with litigation (rather avoidance of). Being CORGI registered even does not always gurantee information. As a RGI I have been refused information when one time I spoke to Baxi. They did not want to commit themselves to information not contained in the manual.

As a non registered person, one has not proven competance. If following Ravenheats directions you were to injure yourself, H&SE would come down hard on Ravenheat. They are only covering their backside.

 

[Alison556]

I'm lost.........................

I think I'm with you all but not, if that makes sense.

The problem is that if the central heating is on, then it doesn't matter how long or short you leave it between demanding hot water, the first burst you get is absolutely scalding hot - and it takes 43 seconds before it goes down to a temperature that you can actually put your hand under without shrieking - yes, I know I'm sad - I timed it!! Even turning the tap on full blast doesn't quicken the water cooling down.

I'm maybe being a bit thick here, but do the primary heat exchanger and domestic hot water heat exchanger not work independantly of each other? This is where I don't exactly know what they look like or how they work cos I've never been in the innards of a boiler. They must do surely? Cos if the DHW HE needs the hot water from the central heating to heat it up, then how does it work if the central heating's not on? Looking at the schematic, the DHW doesn't go through the primary heat exchanger at any point, so it can't be that that's heating it up when the central heating isn't on.................. so why does any of the pipework/water from the central heating need to divert into the DHW heat exchanger?

Am I talking complete crap here? Am I totally confused by the whole thing (probably)!

 

[Agile]

The problem with explaining technical things is that people are likely to half understand and come up with totally incorrect assumptions which make you wish you had never told them anything in the beginning!

Slug seems to be being too helpful! Next he will be giving out John Wilson's 24 hour mobile number!

It is a credit to Ravenheat that they do have one though! Not like all the others who switch off at five to five every night!

Tony

 

[Alison556]

The problem with explaining technical things is that people are likely to half understand and come up with totally incorrect assumptions

When did it become a crime to actually want to learn about something? Terribly sorry for not being a genius and actually asking a question. Must've totally misunderstood what a forum was all about.

which make you wish you had never told them anything in the beginning!

Just as well you've not got that problem of wishing you hadn't bothered - cos you haven't so far - other than to sound like a right condescending git. Do you treat everybody that posts a question like that?

Slug seems to be being too helpful! Next he will be giving out John Wilson's 24 hour mobile number!

Shoot the guy for being helpful. Send him to jail and give him 200 lashes.

 

[Slugbabydotcom]

John Wilson's 24 hour mobile number!

SSSHHHHHH Thats so top secret even I don't know I have it.

There might not be many Ravenheats darn sarf where all the money is. Theres loads round here and I want to know all about them because no one else round here and few on this site have the time of day for them.

I know they are made in Italy from mainly Italian parts but they are designed by an English plumber who did well for himself against the odds.

I am saying nowt else about that now cos I will end up doing a Winston Churchill type speech.
[Cue the music ! Rule Britannia will do]


Anyway my internet's been off all night, so for now I will just try to answer one part of your question for now Alison.

so why does any of the pipework/water from the central heating need to divert into the DHW heat exchanger?

Think about your heating circuit going through the main heat exchanger out to your radiators and back again to be re-heated.
By diverting the water through a plate heat exchanger when there is a call for hot water the now shorter circuit is restricted to within your boiler casing.
The system water is heated up in the main heat exchanger as before but loses its heat to the SEPARATE body of domestic water travelling through your plate heat exchanger.