Valliant ecoTEC 838 / VRC 430 Central Heating pump overrun

[fogster74]

Hi,

First time poster and not very technical, so please excuse my clumsy description of the issue...

I seem to be having exactly the same issue as another poster from back in Nov 2010 (//www.diynot.com/forums/viewtopic.php?t=250697) - that was unresolved then, and I'm not sure what to do. I've searched the forums / online and can find plenty of people with a similar issue, but no resolution.

Background:
1900 Victoria detached house, old combi replaced and resited. Multiple new radiators and pipework replacing most (but not all) the old pipework.

Without the VRC430 installed, the boiler works perfectly (although obviously no room thermostat or clock control). Fires up, all radiators get warm, boiler keeps firing till internal temp hits that set on control panel... lovely!

We then bought a VRC430 and fitted myself. No problem - 430 panel is approx 3 feet from boiler, good signal during install from both external sensor (on North facing wall) and internal panel.

Hot water still works perfectly. Issue is with panel calling for heat - boiler goes through expected status stages (S1, S3, S4, S5)... the internal temperature starts rising (27c,28c,29c...) then suddenly it stops heating and goes into Central heating / pump overrun (S6/S7 - apologies, posting from work so not sure of exact code!).

Removing the wireless receiver module of the VRC430 from the boiler 'fixes' the boiler, from the point of view that I can then at least heat the house (albeit without any control over time or room temp, of course).

I rang Vaillant - they want me to ring back tomorrow when in front of the boiler. Not that helpful if I'm honest... had I paired the transmitter, was the room temp below the thermostat temp etc... seemed to suggest that there was some internal setting in the boiler that may need to be adjusted, but this doesn't seem to make much sense to me.

Also - tried both thermostat and modulator settings in the VRC430 control panel. Made no difference.

Any thoughts / suggestions? Would gladly pay a Vaillant engineer to come out and install - the heating install was done by an elderly gassafe friend of the family - his plumbing / central heating knowledge seems perfect, but he has no idea about new programming systems. Am between Reading and Oxford, if anyone knows someone and it's not something I can fix myself!

 

[gazdaz36]

Is it the 837 combi you have fitted?

If it is why have you got a vr65? This is a wiring centre for a y or s plan system

 

[fogster74]

Oops, that's me trying to be too clever. It's the ecoTEC Exclusive 838 and VRC 430. I'd. wrongly assumed the wireless receiver was called the VR65 - my mistake. I don't have this...

I've edited my original post to remove any reference to the VR65.

 

[gazdaz36]

First 2 things to check for.

1- has the boiler been range rated on the heating to match the demand of the house? this boiler comes factory set at 28kw that will easily heat a large 5 bed house.

2- did you alter the heat curve on the vrc430? for a normal rad system it should be set to about 2.5

 

[fogster74]

Horrible sinking feeling...

1. When we spoke to the plumbing supply company, they gave the impression more was better.....Boiler was not range rated to the house. House is small - approx 1100 sq ft.. Just 7 rads and a towel rail.. Shower runs off combi too so plumber suggested 832 or 838 - as we wanted a decent shower we went with the 838 as it had a good flow rate and we had an 837 in our last place, and which was similarly sized.. Sounds over-specced?

2. Set to 1.2 currently but can change tonight if you think it may help?

 

[Phill Peck]

If you've only got 7 rads then you will probably have no more than 12-15 kw of output needed to rads you need to work out how many kw are reqd then adjust D0 accordingly
Your Instructions will tell you how to do this

Might not solve the problem but needs doing

I'm supprised someone fitting the "exclusive" range wouldn't set it up properly

 

[gazdaz36]

I'd alter D.0 on the boiler to 15 and adjust heat curve to 2.5 then see how it goes

 

[The831Bunny]

Also make sure the heating flow temperature knob is turned to maximum when using a 430. The 430 then controls the flow temperature to the heating.

I'd agree with previous posters concerning D.0 and heat curve. You may find this boiler will cycle quite a bit and overshoot the set point temperature as minimum modulation is 11.2Kw. Thats 10+ radiators in a modern insulated house. To get the benefit of the 38Kw to HW you also need 20+ L/min flow on the incoming water main.

To help the comfort levels in the house I would also try increasing the pump over-run time on D.1 to 10minutes. This will go some way to even out over shoot, but not cure it.

A 832 may have been a better choice I'm afraid

 

[ALEC1]

are the knobs turned to maximum clockwise?

and what is the heating curve?

 

[Bunnyman]

Ahhhhhhhhh! An exclusive! Should have fitted 831 ecotec me thinks , but as 831 said that's the best settings to start with

 

[ALEC1]

i thought the exclusive was vaillants best boiler....what with the dc pump...

 

[Bunnyman]

Rare as hens teeth an the pump always failed, the boiler now comes with normal pump

 

[Agile]

Thats interesting!

Mr Grundfos, at the show, said that soon all boilers will have the permanent magnet pumps and the old ones will not be sold any more.

 

[fogster74]

All,

I just wanted to say a very sincere thanks for your help and advice. When I first posted, I was sitting in a cold, dark house on my own - my father in law passed away last Monday (on my wife and I's first wedding anniversary) - the same day as my wife started her new job, my boss quit (and hence it was the first day with my new boss), and the week that we were due to move in. It's been, quite simply, the worst week imaginable. My wife had gone back to her mum's to sort the funeral and the lack of heating - and fear that we'd wasted £1500 plus fitting - was enough to nearly drive me over the edge.

Then I found you lot....

I adjusted the curve but have not yet adjusted the D0 or D1 - I'll do this when I get back from the funeral on Saturday. What I've worke out is happening (and it's not as I expect), is that the boiler cuts out some time before the room stat reaches temperature. I've not had chance to work out yet if latent heat in the system then continues to warm the house (to avoid the boiler 'overshooting' and heating the house too much), or whether this is a fault of some description, or a failure to have the thing installed by someone who truly understands the boiler. Due to the Father-In-Laws health, weekends were spent over the last few months back in Wales, and it's all been horribly stressful - I just haven't had the chance to do the due diligence, research and checking that I normally would.

I'll definitely adjust the D0 and D1 settings as suggested but would be grateful (just interested to know really) to understand what this is actually doing - if I scale back to 15KW on D0, what actually changes - am I making the boiler behave like a 15KW boiler? Will I not get any advantage over the extra money I've spent on the 838 over a significantly smaller boiler?

Oh - and in reply to the question about the internal heating and water temperature controls - they are turned all the way to the right.

Finally, is it worth getting a heating engineer in to set the system up properly - if so, does anyone know anyone, and what is it that I'd be paying for, and how much would it cost?

Thanks again to everyone for such helpful, open and non-judgemental advice. I'm very, very grateful and would buy you all a beer if I could.

 

[Phill Peck]

You will maintain full hot water output it will only adjust the heating.

If you put @25 kw if heat into a system with around 10-15 kw of output the heat will not leave the system and it will "cycle" due to a high return temperature

I have fitted alot of Vaillant ecotec combis but never an exclusive. Personally I don't see the extra value. But that does not mean you have wasted your money it is a very good product.

Is your installer familiar with this boiler it should have been set up for the system requirements during commissioning