Wiring the Y plan into a combi boiler.. ?

[Useroftheforce]

This is my first ever post - so please go easy on me. I appologise in advance if I have made some fo pa unwittingly!

I am considering installing a new Vaillant 24w Combi boiler in place of the pressurised (converted) Apollo Fanfare unit. This is reliable, but not very efficient, slightly underpowered, noisy and obviously old. The current system has been converted to a pressurised system with the addition of a filling loop and expansion vessel. Apart from that it's bog standard.

Other considerations. I have a very nice expensive shower pump and all the associated, plumbing; tanks, gubbins etc which I am keen to keep in place. I am quite happy for the honeywell Y valve to continue to be used in the old way to do tank HW and CH. The intention is for the DHW on the new boiler would just provide the sinks and bath with hot water. This is becuase I don't want to install much bigger than a 24kw boiler and even though I have excellent mains pressure - 9l pr min at + 35c from input is just not enough for the shower.

Questions: ?

1. I think I know the answer to this one... I presume I need to remove the existing Pump and Expansion Vessel since the new boiler will have them included and there is no easy way to remove them from the new boiler?

2. Is there any reason why the thermostatic electrical input on the new boiler can't be used as per the old switched live on the Apollo Fanfare - thereby allowing me to occasionally heat the water in the tank for a shower from the new combi boiler?

Thanks very much for reading and any answers/oppinons you provide, in advance.

 

[Agile]

Do you have an overheat stat on your current boiler?

All you do is to interface your existing call for heat to the thermostat connections to any new boiler.

Most current boilers have volt free connections and if so that will need a relay with a 240v coil costing a few pounds from Maplins to perform an interface.

Apart from that nothing at all difficult.

Tony

 

[Useroftheforce]

The current boiler has a thermostat on the flow, but I am not quite sure if that's what you mean and therefore if it has one. Not sure why you ask, but if it's in relation to the noise issue. The noise is only from the fan, when it runs and casing which rattles slightly due to the fan vibration, not the plumbing, kettling or any other issues.

Thanks for the wiring tip. The Vaillent wiring shows that it expects the connections to the external timer and thermostat to be 240 / 50Hz. I beleive that is the same voltage as the current Y valve, timer and room stat use. Does this therefore mean, no trip to Maplin? What's a volt free connection? (I am not trying to be dense, I just want be sure I am not missing something important with a foolish assumption.)

This all addresses Q2.

Any replies to Q1?

Many Thanks!

 

[gas4you]

Yes you are correct in your assumption to question 1.

 

[Agile]

The current boiler has a thermostat on the flow, but I am not quite sure if that's what you mean and therefore if it has one. Not sure why you ask,

Thanks for the wiring tip. The Vaillent wiring shows that it expects the connections to the external timer and thermostat to be 240 / 50Hz.


Many Thanks!

I ask because if a boiler is used on a sealed system it MUST have an overheat stat and without one it becomes classed as Immediately Dangerous because it could explode! It should not be used until one is fitted!

If the new Vaillant expects 240v to be applied to the call for heat terminal then your existing controls can be used directly.

A small point is that the controls and new boiler should derive their supply via the same mains isolator so that somebody does not switch off a supply to the boiler and kill themselves on the 240v still inside coming from the still live controls!

Tony Glazier

 

[Useroftheforce]

Ah I see - so if the flow stat died it would just carry on heating indeffinately. That's a great point, I had never thought of that

I inherrited the current system with the house (7 years ago) and it's been a total chamber of horrors to get right I must say.

The boiler was plumbed in the wrong way round for a start... causing kettling. Took me a while to figure that, I just did not expect that!
The rads weren't balanced and full of sludge.
I don't think anyone had done an accurate heat loss calculation since two of the main rads were woefully undersized.
When I had the heat exchanger out of the boiler it was full of burnt paint and all the fins were bent. God knows how that happened. I painstakingly went through and cleaned and repaired them all.
The fan rubber mounts in the boiler had worn to the point that the fan was touching the casing and would not run (a couple of washers has fixed that).
The bypass circuit was incorrectly set, so there was tool little pressure in the primary circuit and it was a tap as opposed to a propper adjustable valve.
The Expansion Vessel had a puncture so was full of water and had to be replaced.
Apart from that it was fine!

 

[Useroftheforce]

Oh yes the entire system uses one electical isolator point so were ok on that point - but thanks for pointing that out and for all the advice so far.