Vaillant 438 s.53 code only with hot water now

[schford]

Hi All,

Have thoroughly searched the forums but can't seem to find the answer for this but it has helped me check things.

Our House is a fairly large 3,300 square foot detached house. I had fitted about 7 years ago a new Vaillant 438 boiler to replace 2 really old crumby ones (one did downstairs and one did upstairs).

But the hot water has never worked properly - The plumber who installed it could only get it to work by having it on 24 hours so I never really worried too much.

However with the cold weather of the last few days I really noticed that the radiators were struggling to get the hosue to 21c - we were lucky to hit 19.

Checking the boiler I noticed that s.53 was showing all the time - some research on here quickly helped me fix that issues - I changed d.0 to 32 from 38, d1 from 5 to 8 and d2 from 20 to 10

I also changed the heating curve from 2.1 to 2.6

Now the house was warming up and the heating worked great!

After sorting that out - I wondered about my hot water issues - so I ran the hot tap for a while and waited for the boiler to kick in - started heating nicely - I did not see what temperature it reached, then quite quickly I got s.53 code again - which I think means the differential between temp in and temp out is too great. Waited for that to cycle it repeated the process again once more. Third cycle it seemed to heat up for much longer this time and now the code was s.28 the anti cycle, this has now repeated 3 times - each time wwater goes up to 82 or 83 degress heating stops and s.28 is displayed.

Another issue I noticed is that when all this was going on with the hot water - the radiators were not getting any heat ad the boiler seemed to b locked into hot water mode.

I do not think that the plumber when he installed the system changed the circulation pump to a more powerful model - though this weekend I will take the cupboard back off to gain access to the pumps to check.

That said - has anyone any suggestions on how I can improve the performance of the system - specifically the hot water?

So that it stops the s.53 code and stops locking out the heating when it takes an age cycling to heat up the hot water?

Many Thanks

Stuart

 

[Biggles..]

What size pipes come off the boiler
What is your heating pump?

That'll be your problem

 

[Biggles..]

Who was the driving force behind the weather comp choice as the VRC400/43/440 don't ho well with the 4xx series boikers
Have your the vr65/66 fitted?

 

[The831Bunny]

You probably have Vaillant's weather compensation (470?), so the HW & Heating circuits are independent. The default settings are set to the system having HW priority. This means while your cylinder is being reheated, central heating is turned off. This is normal. It has the benefit of each circuit having their own settings adjustable to suit your situation, and yields the best efficiency and comfort.

Could you post back how many radiators/towel rails your house has, and the make and size of the hot water cylinder. Also as mention by LeeC, the make & model of pump too. I'm afraid it sounds like its never been set up correctly...

 

[schford]

Thanks so much for the feedback guys - I am going to have to take out the back of a cupboard and move a tumble drier and washing machine to get to the circulation pump!!

I am working form home tomorrow - so will have to do it then, think the MRs would kill me if I started taking apart the utility room tonight!

In terms of questions in order

1 - I will take off the cupboard back and move the washing machines tomorrow - that should give me access to the circulation pump and to see what size the pipes are.

2 - I have absolutely no idea where or how the VR65 was fitted - it is not visible by the boiler - so I suspect its behind the false backed wall.

3 - I was promised that the VRC 400 would save on gas usage and as were are on an LPG tank - I was all up for that!

4 - We have the VRC 400 which was indeed weather compensating - I believe it was their first attempt (is really not user friendly!) and was replaced a few times and the VRC47o is the latest model!

5- I bet if the hot water didnt take so long to heat up then it would be the best way of doing it - I remember filling up a blow up hot tub for kids last year, it took hours to heat up the cylinders and so the house got freezing as there was no heating - man was I in the dog house!

6 - We have 8 Radiators down stairs and Upsatiars we have 3 towel rails radiators and 9 radiators.

7 - we have 2 no name hot water tanks with what appears to be sprayed on insulation that look to be about chest height - with cold water tank in the attic.

Thanks again everyone for the help - really appreciate it - and if anyone is near to Windsor / jct 13 of the M25....it probably is due a service as well.

cheers

Stuart

 

[The831Bunny]

Ok, here are a few basics for staters.

If you have any Vaillant weather comp controller, set BOTH HW & Htg knobs on the boiler need to be set on Max. Both temperatures are then set set on the VRC400.

As you have 20 heat emitters, start off with setting:
D.0 to 28
D.1 to 15 (yes 15)
D.2 to 20
D.70 to 0
D.71 to 78
D.72 to 240
D.73 to 0
D.75 to 45
D.77 to 20
D.78 to 85

Set your DHW temp to 55C on the VRC400 and the heating curve to 2.4.

If you can see/find the pump then make sure its set on maximum.

That should improve things... Good luck

 

[The831Bunny]

Sorry, now re-reading your post above, it's very possible , if you can't find a VR65 box near the motorised valves, unless your cylinders are together in the airing cupboard your system WILL NOT work connected to a VRC400. At the time too when your boiler was installed, Vaillant VR domestic 'boxes' cannot control two separate cylinders and a heating zone.

 

[schford]

Will go try those - but quick feedback

1 - I had a bill for a VR65 so I am sure it is in there some where

2 - The 2 cylinders are pretty dumb they are right next to each other in the airing cupboard and there is a single pipe feeding them (it splits) and a single flow back out (with a 2 into 1 connection)

A bit more info - the old fashioned dumb hot water tanks still have their original thermostat on the side and that is how I set the temperature for the hot water - the controls on the vrc 400 dont do anything in regards to setting hot water temp.

Cheers

Stuart

 

[Biggles..]

How may motorised valves on the cylinder coils?

 

[schford]

there are no valves in the airing cupboard connected to the cylinders. I can only assume there is a single one near the boiler - but will check tomorrow.

 

[schford]

All changes made - seems great so far! Ran the hot water tap for 10 mins to give a decent drain to cylinder.

Boiler kicked in and steadily increased temperature up to 86 wit hot water symbol flashing then slowed down - temp dropped to 81 - then kicked in a bit more up to 86

This repeated for a while until (I assume) cylinder back up to temp then it stopped!

Thank you so much - hopefully it keeps on working well

One funny I have noticed is that the 2 radiators in the lounge - now only the first one gets hot, probably due to difference in temp or flow or something, will re-balance tomorrow and report back!

Stuart

 

[The831Bunny]

That's good news. Not knowing the coil ratings in the the two tandem cylinders, and indeed if there are two motorised valves feeding them or not, the HW load could be significantly less than 20Kw (D.77). Try experimenting with D.77 and reduce to a figure that prevents on/off cycling in all but the last 5mins of reheating. Maybe start at 16.

The problem with using standard cylinder thermostats with a VR65 box is the that the boiler doesn't 'know' how hot the stored water is, and also how quickly the temperature is falling or rising. Using the VR10 NTC temperature probe (which came in the box...) gives this extra level of control, this virtually eliminates on/off cycling at the end of a cylinder recharge. It also gives the boiler the function of learning the best time to turn off the reheating to prevent overshoot.

Sadly I can't think of a sensible way to apply this to two tandem cylinders. If they were truly piped in parallel putting the VR10 on one cylinder would leave the other cylinder to end up with 'approximately' the temperature of the first, but that's not very safe at all. Maybe a standard zone valve on your 2nd cylinder connected to its existing cylinder stat would act as a safety backup set to say 60C.

Just thinking out loud...

 

[Biggles..]

If you pipe the cylinders up as a Christmas tree to all connections , as long as the cylinders are identical then you'll get exactly the same temp in all of them.
Least then if you put the vr10 in a pocket on the outlet you'll have s pretty accurate idea of DHW temp.

 

[schford]

Re-reading my description of current hot water heating it might look as if it is cycling - its not

The heating comes on strong(you can hear a nice roar) until it gets to 85/6 then you can here the heating back off a little but still on until temp drops to 81ish then comes on strong again - it repeats this until it stops but never cycles even at the end.

Given that the hot water is now not cycling with it set to 20 and it seems ot heat up well - would I be right in thinking I can leave alone?

Unfortunately I have no idea where the VR10 has gone or why it was not fitted in the first place or even if there are enough free wires in the cable run from the cylinders back to the boiler!

The boiler is due a service though - how can I find some one around TW19 who is as knowledgeable as you guys?

Thank you both so much for all the help!

 

[The831Bunny]

If you pipe the cylinders up as a Christmas tree to all connections , as long as the cylinders are identical then you'll get exactly the same temp in all of them.
Least then if you put the vr10 in a pocket on the outlet you'll have s pretty accurate idea of DHW temp.

Absolutely Lee, but it would only take the coil to be blocked or a balancing valve to be shut on the first cylinder with the VR10, and the second cylinder would reach the primary temperature... VR10 needs to be 1/3rd of the way up a cylinder to sense the drop.