ultacom 38hxi problem

[osi55]

hi I've a property with two ultracom boilers, which used to heat up fine, this year not as well, when I look at the boilers I notice that one of the boilers is showing a steady 75 deg which is what its set at, but the other isn't reaching its temp which is supposed to be the same, it does try every ten minutes or so and then goes out, it comes on say at about 60 or so and climbs up to the 75 deg mark with all five lcd burner indicators on, I assume at max ? but when it reaches 75 instead of dropping down to around two and holding at 75 , like the other one does, it seems to keep going and then goes out and it all starts over again, my plumber says he's checked the stats and the pumps and there ok he also tells me he has range rated it to 7 kw? and it still does it, not sure what that means but he says that means its not the pumps

any ideas

 

[Agile]

It sounds like a flow problem but without full details of your system we cannot advise.

You say you have had a plumber there but he obviously cannot understand whats wrong.

My advice is to get a competent heating engineer who can solve what is probably a very simple problem.

Tony

 

[dcawkwell]

Sounds like it is working right and you have two boilers working
as a cascade. The second boiler coming on when the first boiler
isn't keeping up with demand.

 

[osi55]

It sounds like a flow problem but without full details of your system we cannot advise.

Hi Agile

system is two 38hxi with two grundfus ups 25-55 pumps piped reverse return into header then from header to radiators through another 25-55
there is a bypass on the radiator circuit just after the pump
the pipe work comes out of boilers in 22mm then 28mm then everything is 35mm apart from llh which is about 65mm it has a tank and they just do heating which is about 30 rads

You say you have had a plumber there but he obviously cannot understand whats wrong.

My advice is to get a competent heating engineer who can solve what is probably a very simple problem.

I've had a few but I'm getting varied solutions, so I thought I'd see what you guys suggested before I commit

Tony

 

[Agile]

Oh dear!

Calling people to give you a free diagnosis is unlikely to work!

Firstly those willing to come like that are going to be those short of work and usually thats because they are not very good.

Secondly anyone who is any good will always charge to come and diagnose the problem! I do!

Tony

 

[osi55]

we've paid £1600 so far - hopefully its nearly there! and hopefully it is a very simple problem, cause I don't want to spend too much more !

 

[JayPage]

are the boilers twinned? As in a Lead-lag setup?

 

[dcawkwell]

we've paid £1600 so far - hopefully its nearly there! and hopefully it is a very simple problem, cause I don't want to spend too much more !

£1600 for what. To install the boilers or to come around and not fix a problem?

 

[osi55]

no its not lead and lag its one wireless roomstat! its either on or off it switches both boilers on or off.

the 1600 hundred was for an upgrade from what we had originally, it worked well for short while, still working a LOT better than it did, just with one boiler, changed from one pump and no header, to three pumps and a header, boilers were doing f.a. before, plumber said because differential was too big? now one works the other don't

I'd like to see them both maintaining what they're set to or is this not possible?

why is one boiler able to see it has reached temperature and reduce its output accordingly and the other cannot?

 

[dcawkwell]

no its not lead and lag its one wireless roomstat! its either on or off it switches both boilers on or off.

the 1600 hundred was for an upgrade from what we had originally, it worked well for short while, still working a LOT better than it did, just with one boiler, changed from one pump and no header, to three pumps and a header, boilers were doing f.a. before, plumber said because differential was too big? now one works the other don't

I'd like to see them both maintaining what they're set to or is this not possible?

why is one boiler able to see it has reached temperature and reduce its output accordingly and the other cannot?

My guess is both boilers are running and modulating down
to their minimum setting. At which point for some reason one cuts off.
That boiler will not re-fire for 2-3 minutes or whatever the setting on the boiler is. It then fires and brings it back to temperature.
Sounds like it's working to me. If the place isn't heating up the problem is elsewhere in the plumbing not the boilers. A test for this will be to set the one that is cutting off a couple of degrees higher. You should then find that
the other boiler starts cutting off before reheating.

 

[osi55]

we've tried varying temperatures, one boiler runs upto say 75 and then drops back to low flame enough to maintain its set temp

the other doesn't reach its set temperature THEN modulate down - it just keeps on powering through until it gets about 3or4 degrees above what were asking for then it drops out totally and sits and waits for about five minutes or so by which time the read out on the front has dropped to about 60 which I guess must be the return temp? then it tries again gives a blast takes it up to around 3or4 above and poof! drops out again!

this takes around 30 seconds - short thirty second blasts every 5/10 minutes
are pointless

 

[dcawkwell]

we've tried varying temperatures, one boiler runs upto say 75 and then drops back to low flame enough to maintain its set temp

the other doesn't reach its set temperature THEN modulate down - it just keeps on powering through until it gets about 3or4 degrees above what were asking for then it drops out totally and sits and waits for about five minutes or so by which time the read out on the front has dropped to about 60 which I guess must be the return temp? then it tries again gives a blast takes it up to around 3or4 above and poof! drops out again!

this takes around 30 seconds - short thirty second blasts every 5/10 minutes
are pointless

Little flow going through the boiler. Thats why it heats up so quick.
That is why it overshoots the set temperature.
Problem is the plumbing not the boilers.
I suggest test each boiler working on it's own with the valve to the other boiler shutoff. Does each boiler work ok on it's own?

 

[osi55]

ok I'll let you know what happens

 

[osi55]

checked it today and both boilers working at a steady 75!

however I expect after the boilers shut down and re-start one will have trouble and start to over shoot.

does this mean air trapped in heat exchanger?

 

[dcawkwell]

checked it today and both boilers working at a steady 75!

however I expect after the boilers shut down and re-start one will have trouble and start to over shoot.

does this mean air trapped in heat exchanger?

No it means that no flow is going through one boiler when the other is operating.
Plumbing is at fault. If one boiler is maintaining the temperature then it is working ok nd the other boiler isn't needed as if there was too much demand the first boiler wouldn't
be able to maintain the 70 degrees. If the house isn't heating up properly the plumbing is at fault.