Nightmare Boiler Installation - Mains Pressure Coil

[Tabs101]

Hi

I am having a nightmare with my boiler installation company. I was quoted for a straight conventional boiler swap as my current tank system is really good.

They have installed a Vaillant ecoTEC Plus 418 boiler and they cannot wire the programmer or thermostat to work. After several visits they have told me that they will need to install a new tank system to make it work correctly (costing me more money).

I currently have an open vented thermal store with a mains pressure coil that has two pumps (water and heating) with no valves. The water pressure I get form the current system is amazing.

Apparently there is a problem with my current system and the pump override on the boiler and if they wired the system to work it would not comply with building regs.

Any advice would be appreciated. If anyone knows how to wire the programmer and thermostat to this boiler/system then please let me know so that I can inform them before I have to pay out for a new tank system.

Thanks in advance.

 

[wannocks]

If you have described your thermal store correctly:
One pump will be between the boiler and the thermal store, this is the one the boiler should control. The other will be for circulating the water through the radiators and should be controlled by your programmer/ room thermostat. The hot water simply flows through the coil immersed in the store of hot water and is not pumped.
There should be a control thermostat and an overheat thermostat on the store that should control the boiler's 'call for heat'.

 

[Tabs101]

Hi, thanks for the reply.

I think that is correct. I have attached 2 photos showing the pump and tank.

 

[Tabs101]

Apparently there is a problem because the new boiler has pump override where the boiler will switch off and the pump(s) should keep running.

They are saying that the new boiler cannot function with the current system that I have. Surely modem day boilers should be compatible with older existing systems (installed in 1997). You can still purchase Unvented Mains Pressure tanks (I think).

 

[Johnmdc]

As wannocks says the primary pump should be wired directly to the boiler so that it can control the over-run, the boiler will also need a permanent live to it.
The boiler and hot water will be controlled by the clock and tank thermostat.
The heating pump will be controlled by the clock and room thermostat.
If you have a 2 channel clock for the heating to work you will also have to have the hot water on, which was how it would have worked before with your old boiler.

 

[flameport]

They are saying that the new boiler cannot function with the current system that I have.

What they really mean is that they don't know how to make it work properly.
Wiring may need a few minor alterations, but it CAN work with the new boiler.

 

[Tabs101]

Thanks for all your reply's so far.

This information is perfect as the general manager and the electrical manager of the company are coming on Monday to discuss options.

If anybody has anymore comments then please post so that I can talk it through with them.

 

[bernardgreen]

As Wannocks said only one pump needs to be controlled by the boiler. That is the pump that circulates hot water from the boiler through a coil of the store tank and back to the boiler. That would be controlled by the boiler in response to the thermostat on the tank.

The other pump circulates water through the radiators with heat from the store tank and is ( should be ) controlled only by the room thermostat and a timer for when heating is required.

The pumps are ( or should be ) controlled by two totally separate control systems.

Most important is that boiler need not respond to the room thermostat, If the room thermosat calls for heat then one could say the boiler should fire up. That is not the case with a heat store tank. If the system is as a I think it is then the boiler fires up only when the store tank is not hot enough to heat the house. Heating the house cools the store tank, when the store tank becomes too cold to be able to heat the house then the themostat on the store tank operates to fire up the boiler.

My bet is that the wiring of these two separate control systems is wired in such a way that they appear to be one system. Cables run side by side and sharing a box of terminals could lead the in-experienced technician to believe they are looking at one single complex control system when it is in reality two very simple control circuits

 

[Dan Robinson]

Further to this, there are often two thermostats on the store. One activates the boiler and other holds the boiler on/off to prevent nuisance firing on small draws. Usually a simple relay coordinates this. Had a wiring diagram somewhere but can't find it.

This is not always necessary if the stat on the store has a wide hysteresis or is adjustable.

 

[Agile]

Tabs, it is a very simple matter to wire your new boiler to work properly. We all know how to do it. But your installers apparently don't.

How do they come to be doing this work for you? Did you choose them or something else?

Be aware that a modern condensing boiler is never very efficient when running a thermal store like that because they are designed to have a stored water temperature of about 85C and current boilers don't give more than about 75 C and to do that they are not condensing much.

Tony

 

[Dan Robinson]

have a stored water temperature of about 85C and current
boilers don't give more than about 75 C and to do that they are not condensing much.

Sorry Tony - you're wrong on most counts... apart from yes - they will condense less.... btu I had my steamer running a 300 store condensing into a 2 litre sprite bottle.... Needed emptying quite a bit in the winter.

Store was heated to 60 degrees at the bottom with the flow set to 70 on the boiler. Hot water through a big plate was fine.

Never did get round to playing with dual flow temps properly... but now i have an OT bridge, I might one day reinstate the store and try again.

 

[Dan Robinson]

Oh - had a Bunny driving an ACV yesterday to set up - can get them to 80 degrees with a few correctly pressed buttons.

 

[Dan Robinson]

Not my installation - I was there to sort out the original installers myriad of cock ups. Not least putting all 3 UFH zones on the zone one terminals of the UFH controller

 

[Agile]

Sorry Tony - you're wrong on most counts... apart from yes - they will condense less.... btu I had my steamer running a 300 store condensing into a 2 litre sprite bottle.... Needed emptying quite a bit in the winter.

Yes, but your oversized plate will probably be a lot more effective that the OP's HW coil and probably not very comparable.

I thought that you had used the two flow temps with a Tupperware box!

Now he will not be surprised if its not quite as good as he has experienced before.

Tony

 

[Dan Robinson]

I did try it but not for long enough to get any tangible data, plus there was an undetected problem that kept the bloody plate shunt pump running effectively destrating the store.

Point is, For all we know..... which is very little in terms of the OP's set up.