Vaillant 438 problems

[eagleeye]

Have just installed a new boiler for a customer (well i did on Monday anyway) and have had nothing but problems with the system. Fitted new boiler and did a full power flush (before new boiler was fitted !!) and when all fired up i kept getting S.54 code. seemed as though it was air so the next day i drained down and fitted AAV's above boiler (even though flow and returns went straight up) to see if this sorted the problem. No luck !! then converted it to a sealed system as i thought this may help (and is a better system anyway) still no luck. Carried out another powerflush as advised by Vaillant technical. Even fitted a new pump just in case. Still no luck. Spoke to vaillant again and we got it down to a maybe on the flow though the mid position motorized valve. so converted to 2 - 2 port valves to see if this made a difference. Yes it did but still not right as return is hotter than the flow and if i open up all trv's instead of just ground floor it goes to S.53 again. Could it be that the Grumfos 15-60 pump isnt big enough ?? it is a 19 rad system in quite a big house and long primary and returns from boiler to pump (about 20M horizontal, then for downstairs circuit it runs the same way back and drops down by the boiler). so far i have been on it 3 days and its doing my head in. I will call Vaillant again tomorrow to see what they say, but just thought i would see if anyone had any ideas. Before you ask, I have checked the flow and returns are the right way round yes. Helpppppp

Thanks

 

[phpaul]

Have just installed a new boiler for a customer (well i did on Monday anyway) and have had nothing but problems with the system. Fitted new boiler and did a full power flush (before new boiler was fitted !!) and when all fired up i kept getting S.54 code. seemed as though it was air so the next day i drained down and fitted AAV's above boiler (even though flow and returns went straight up) to see if this sorted the problem. No luck !! then converted it to a sealed system as i thought this may help (and is a better system anyway) still no luck. Carried out another powerflush as advised by Vaillant technical. Even fitted a new pump just in case. Still no luck. Spoke to vaillant again and we got it down to a maybe on the flow though the mid position motorized valve. so converted to 2 - 2 port valves to see if this made a difference. Yes it did but still not right as return is hotter than the flow and if i open up all trv's instead of just ground floor it goes to S.53 again. Could it be that the Grumfos 15-60 pump isnt big enough ?? it is a 19 rad system in quite a big house and long primary and returns from boiler to pump (about 20M horizontal, then for downstairs circuit it runs the same way back and drops down by the boiler). so far i have been on it 3 days and its doing my head in. I will call Vaillant again tomorrow to see what they say, but just thought i would see if anyone had any ideas. Before you ask, I have checked the flow and returns are the right way round yes. Helpppppp

Thanks

ive had it that the thermistors were iffy causing th s53 you could down rate the boiler or reset the boiler settings

 

[glenno1]

Are you sure pipework is right,as it sounds like heat is not getting away from boiler fast enough

 

[chris watkins]

15/60 will almost certainly be to small, the boiler heat exchanger will take out around 4M head from the 6M pump leaving only 2M to overcome the system resistant's. I know you have cleaned the system but the very small waterways through these boilers do cause all sorts of problems, any small restriction around the whole system that reduces the water flow rate through the boiler will lead to boiler controls holding off as there is little temp diff between F&R.
I know its a bit late but next time install Low Loss Header.

 

[eagleeye]

Thanks for the reply guys. problem with the flow / return all sorted now. Turned the output down to 32Kw and it just about stayed on without going to S.53. Have worked out volume of water in the whole system and it is about 370 ltrs. So it seems like I will need a bigger pump. Thing is, is that when the system was put in the plumber thought it would be a good idea to tee the radiator return into the primary return in the concrete floor after the main cylinder return so a couple of the upstairs rads are getting hot when the hot water is on. Because they didnt bring the primary return out the floor (well only about 2 inches of it straight from the cylinder) i now cant get a bypass on the primaries. What I now have to do is to remove the cylinder (all of the 300 ltrs of it) as well as 2 monsoon pumps (so i can get the cylinder out) then carefully chase up the floor around the pipes and make alterations to pipework. Nightmare of a job but it has to be done right.

 

[chris watkins]

eagleeye by name but not by nature ?? You will have to put this one down to experience. LOL
Did they need the full 38kW for the heating or was the boiler over sized any way ? Got to take care turning it down if it is now too small they bought & paid for 38 you have now fitted a 32kW.
I don't quite see how the system volume relates to a pump size as it is the hydraulic resistance & flow rate across the system that should be used ? If the 15 / 60 is to small, you may find that there is not enough pump pressure left to open an auto by-pass after you have gone to all that trouble to install it. Thats the trouble with these bigger systems they can be a bit more complicated.
The problem with the rads getting hot can normally be solved by installing a non-return valve (not a check valve) if you can access the pipe work before the rads, to check, the returns to the rad's should getting hot before the flows, if so cut the valve in so it is in the normal direction of flow which will stop it.

 

[eagleeye]

thanks for your comments chris but yes they did need a 38kw boiler as there are 20 rads on the system with only 3 being single and a 300 ltr hot water cylinder. question to pipe runs, yes they are very long. primary flow and return are at least 20 mtrs and then the downstairs heating circuit follow the same route back and drop down by the boiler. As the auto by pass goes, fitting a 25/55 pump to overcome the problem of the circulation im sure this will be enough pressure left to open the bypass for pump over run. Have been in the game 20 years so experience is not a problem here. Never had a problem this bad before. But i wont let it beat me. Reason for rads getting hot when hot water only is called is cos of the reverse circulating. Hence the reason for me wanting to alter the pipework so the heating return is teed into the correct position of the primary circuit and so that the primary return actually comes out of the concrete floor upstairs.