Boiler heating hot water every 10 min

[matz]

we have a newish Valiant non combi condensing boiler.

Currently due to warm weather, the CH is set to off. The DHW is set to continuous and the boiler fires up every 10 minutes without fail over 24 hrs even though sometimes no hot water is being used - I'm guessing the boiler is clicking off on its stat as it makes a few rumbling noises just before it switches off.

The hot water cylinder is approx 15 to 20 yrs old and is traditional copper with foam outer. The water is hot when run from tap.

My question - should the boiler be continually clicking in like this? it seems like theres a problem somewhere? maybe hot water tank coil partially blocked (water flow being disrupted) or furred up so heat from boiler not being dissipated?

any thoughts

 

[Rampage77]

You should have a motorised valve located on the system (near cylinder normally) this could have a faulty micro switch, or stuck which could be causing the boiler to fire up.

 

[Agile]

I suspect that your controls are not set correctly.

The cylinder thermostat should be at 60 C and the boiler at 70 C or higher.

A DIYer could reset these but a heating engineer with the test equipment could do it more accurately.

Apart from any disturbance you are wasting gas with it like that.

Are you having the boiler serviced regularly? A good engineer will check these settings at a service!

Tony

 

[matz]

cylinder temp is 50. Boiler is set to about 63. If boiler is set higher it kettles as it approaches that. Boiler is fully serviced. CH and DHW operates with a Myson diverter valve. This is the second one we've had installed over 3 years and it was letting hot water through into the CH (even though CH was off) but the engineer adjusted it and stopped that. He did say the Myson valves were rubbish and we needed a different type.

So unlikely to be an issue with the the coil in the cylinder then?

 

[Agile]

To prevent legionella problems the advice is to operate the cylinder at 55 C to 60 C.

But if you can manage at 50 C and are aware of the risks then that's fine. Some would say increase to 60 C once a week!

You don't say your boiler model but it should be an Ecotec if its "recent" meaning less than six years old.

But that model should never kettle ???

My expectation is that the cylinder thermostat is never switching to the satisfied condition and turning off the boiler.

If you turn the cylinder thermostat down then does the boiler eventually turn off and stop cycling?

Is the boiler display showing 63 C while its reheating the hot water?

Tony

 

[matz]

To prevent legionella problems the advice is to operate the cylinder at 55 C to 60 C.

But if you can manage at 50 C and are aware of the risks then that's fine. Some would say increase to 60 C once a week!

You don't say your boiler model but it should be an Ecotec if its "recent" meaning less than six years old.

But that model should never kettle ???

My expectation is that the cylinder thermostat is never switching to the satisfied condition and turning off the boiler.

If you turn the cylinder thermostat down then does the boiler eventually turn off and stop cycling?

Is the boiler display showing 63 C while its reheating the hot water?

Tony

wow didnt know about a min temperature so have put it back up to 60 on the cylinder stat

when turning the cyl stat down to nil, the stat clicks, the light goes out on the diverter valve and the boiler doesnt run.

its an ecotec 415 about 2 yrs old. Already had the heat exchanger changed by Valiant once.

the DHW temp on the boiler is set to 63. We did have it at quite a bit higher than that but kettling was much worse. When I say kettling, its rushing noises and light banging noise.

 

[Steelmasons]

Was fitting the ecotec back in 2006 , model has been around 10 years or so.

 

[Agile]

Its considered perfectly safe to have the HW at 55 C.

But what temperature does the cylinder stat turn the boiler off at?

They are often not well calibrated.

Should be about 1/3 of height above the bottom of the cylinder.

Tony

 

[matz]

Its considered perfectly safe to have the HW at 55 C.

But what temperature does the cylinder stat turn the boiler off at?

They are often not well calibrated.

Should be about 1/3 of height above the bottom of the cylinder.

Tony

re. cyl stat turning boiler off - I had cyl stat at 60 with the hot water heating up as just had a bath. Waited till boiler fired up then turned stat slowly down to nil. Boiler took 20 secs to cut out. Conversely, turned stat down to nil, waited till pipes had cooled a bit then turned stat up to 60 and there was a 30 sec delay in boiler firing up. Cyl stat is 3rd way up the cyl.

 

[Agile]

You need to check the cyl stat when the cylinder has reached the set temperature!

Tony

 

[matz]

ok heres some more info. DHW has been heating all night with stat at 60. No one has used hot water, I've run the hot water tap for 3 mins until it would typically get hot, poured hot water into a glass and stuck a thermometer in it and its reading 37c.

PS the heating pipe going into the cyl is hot when boiler is firing and the one coming out is slightly less hot

PPS the upstairs rads in bathroom and ensuite get hot as well even though heating is off on the room stat.

 

[Agile]

You said the hot water was "hot" !

37 C is blood temperature and just warm and far too cool for me to take a shower as I like 43/44 C.

So we need to know the temperature of the flow and return of the heating coil !

Normally with a contact temperature meter ideally a proper one using a "K" type thermocouple.

Tony

 

[matz]

well I suppose hot is subjective. Its only just dawned on me today that its not hot enough. certainly now measuring at 37c - thats clearly not "hot". I will try lay my hands on temperature meter though inclined to call engineer in tomorrow.

Out of interest, when boiler fires up on DHW only it goes from 40c to 65c which takes 20 seconds then shuts off for 10 mins then repeats that cycle. Is this how it should be?

Many thanks for your help, I do appreciate your input - sorry if I am giving duff info...

 

[Agile]

When the boiler is only heating the HW then it should burn for at least 2-3 minutes.

If yours is increasing the flow temperature so fast then there is a restricted flow for some reason.

As well the return is probably not increasing in temperature either.

Tony

 

[slapper]

If it cuts off after 20 seconds and then comes on after 10mins, then you've a circuitory problem on Flow/Return or a partial blocked coil on cylinder. That's why its kettling on temp over 60c