Any plumbers here who.can give advice

[graduate_owner]

Hi all,
I have a Grant oil boiler with a Riello burner, which is 2 years old. It was serviced about last April and hasn't had much use over the summer because we don't use it for domestic hot water. Now the problem - I noticed it seemed to be cutting out regularly so I timed what was happening. Once the rads are hot the boiler runs for 2 minutes then cuts out, rests for 2-3 minutes then starts up again. I was thinking either a thermstat problem or it is set to give too high a heat output for the load. The plumber who installed it and serviced it is so busy he doesn't return my calls.
Can anyone offer any advice please?

K

 

[misterfish]

Would you expect the boiler to tun continuously? With the oil and gas systems I have seen (and used) the burner ignites and heats the water that circulates around the rads by means of a pump. Once the water is to temperature (set on the boiler) the burner goes out and the water circulates. As the temperature of the wate drops the boiler fires up again until the water is at the required temperature at which time the burner goes out. The system continues this cycling.

Are the radiators too hot - if so then it sounds like the temperature set atthe boiler is too high and needs to be set lower. Also it has been pretty cold of late so I would expect the boiler to need to keep topping up the heat in the system.

We used to live in Upper Chapel between Brecon and Builth on the old mountain road and knowhow cold it could be some times!

Misterfish

 

[sunnybob]

As above.. The boiler is working exactly to plan.

 

[Doug B]

Is this is not how your system has run previously? I would ask if you have a room stat & if so Is it functioning correctly.

As stated above cycling of the boiler is usual when the rads are up to temperature but not the rooms they are in are not, but once the rooms are up to temperature the room stat should shut the boiler down.

 

[HappyHacker]

While the boiler is cycling as it should I would question the frequency. While I am not familiar with your boiler I have had and fixed a few oil and gas boilers and normally the boiler would be off or on for at least 15 minutes even when the rads are hot.

At two minutes on/off it is in my opinion too short and is indicative of an overly large boiler for the load (if it did not do this in the past it is not the problem), blocked radiators/pipes (is the bottom of all the rads getting hot?), a blocked or faulty pump, a faulty controller on the boiler, faulty thermostats on the boiler or possibly some combination of the above.

I think you need someone on site who can work through the possible faults to a diagnosis.

 

[sunnybob]

The cycling rate of the thermostat determines how often the boiler lights. A digital stat is far more sensitive than an old analogue one.
If its digital it could easily respond to a few decimal points of one degree (this is usually alterable in the stat program). An older type will respond to 5 or even 10 degrees difference.

Its very unlikely to be an over sized boiler as that would have increased the install costs.

I spent many years working with gas fired, but dont have much experience with oil fired. It would be worth checking if the boiler is "self modulating". This means that as the water temp gets close to the desired temp, the boiler reduces the fuel used and basically "creeps up" to the set temp., rather than the full on -full off mode that you are seeing. There might be a way of changing between the two modes. Study the handbook.

 

[graduate_owner]

Thanks for the suggestions guys. Just to clarify, we replaced an existing 19 year old boiler with a new condensing one, and fitted a new circuation pump at the same time. It is a conventional system, i.e. header tank in attic. The thermostat is in the (large) hallway and set to about 14 degrees which it rarely reaches so no issues with that cutting out too often. It is an analogue type.
The building is a barn conversion with high, vaulted ceilings in an open plan lounge kitchen diner. I replaced a radiator in there with one of three times the previous output when the boiler was changed because it is a big space to heat and is not very warm in winter - just a bit below comfortable when it gets cold outside. So it isn't a case of the room getting hot and the radiator having nowhere to unload the heat.
I don't think the boiler cycling should be as rapid as it does though, hence the post.

Does this offer any further insights into the issue? Again any further opinions would be gratefully accepted, before I look for another plumber.

K

 

[sunnybob]

In that case, theres a possibility the separate circulation pump isnt big enough for the boiler, causing the internal safety hi limit stat to shut down untill theres enough water movement to lower the temp inside the boiler.
Do you have thermostatic valves on the rads? If so, are they adjusted to maximum? If you do have thermostats on the rads, there should be one rad (usually a bathroom or master bedroom) that does NOT have a stat valve. Other wise all the rads will shut down and cause the problem you have.

 

[graduate_owner]

The TRVs on the rads do shut down in the bedroom but in the hall and lounge the rads are still hot so the TRVs are not shut down on those rads, which is the bulk of the property. The boiler cycles even wen the temperature control is at maximum. From the suggestions, it looks to me that either the pump is not up to the job ( it's a Grundfoss, cost about £120 so not a cheapie), the boiler stat is faulty and cutting out at too low a femoerature, or the boiler output needs reducing. Whichever, it looks like a job for a plumber - the boiler nozzle can be changed but I think it will need setting up to burn efficiently then.

I will check the bottoms of the rads though, to see if there may be some sludge causing blockages.

Anyhow, many thanks to all for taking the time to offer advice. Much appreciated.

K

 

[sunnybob]

You didnt confirm you have 1 rad that DOES NOT have TRV's. This rad should have lock shield valves both sides and be left fully open.
The fact the rad is hot is not enough to ensure the water is circulating fully.
Some "plumbers" are not aware of this. I had central heating installed last winter because I am old and lazy and could afford to pay someone instead of doing it myself.
The plumber has been in business for 20 years and did not know which way round to fit TRV's. He had to come back and swap 6 sets over.

 

[misterfish]

The Grundfoss pumps I've had on two previous heating systems had a rotary switch control on them to allow three speeds. I seem to remember the idea was to try the low speed and if that wasn't adequate then the mid speed and ultimately the fast speed if still inadequate.

Misterfish

 

[Deejay]

Morning K

When the boiler cuts out does the pump stop (possibly after a few seconds)?

If the pump remains on it would imply that the boiler preset max temperature has been reached but the system is still calling for heat.

If it stops and remains off until the boiler restarts, that implies that the system thermostat stops calling for heat.

Cheers

Dave

 

[graduate_owner]

Dave, the pump keeps going after the boiler has cut out so, as you say, sounds like high temperature thermostat has operated. I don't know if that means the thermostat is faulty or the boiler output is too high - or something else!! The pump has 3 speeds, on two settings. Setting one gives 3 speeds regardless of circumstahces. Setting two gives three speeds which, from what I can make out, will automatically vary with load to be more economical on electricity. I have tried all settings but the boiler still cuts out. I have left it on high speed.

K

 

[Deejay]

Afternoon K

Have a poke around on the Grant website. You might find the user manual there, which should tell you how to set the maximum flow temperature. With a two year old boiler, I'd be surprised if you can't set it yourself.

If you can't find it, give them a call. I nearly bought a new oil boiler from them a few years back and they were most helpful.

Cheers

Dave

 

[Doug B]

Was the system flushed before the new boiler was fitted?

 

[graduate_owner]

When I drained the system ready for the plumber, the water looked clear so I didn't do a flush. I fitted a magnetic filter and checked after a few weeks, and there was very little debris. Also the rads are warm at the base so I'm assuming all is clear in that respect.
The boiler handbook gives some details on varying the heat output, but it involves fitting a different jet and re-setting the mixture which needs a gas analyser.
The only other thing I can think of is, now that the kids have flown the nest, we don't have all the rads on. I shall try turning all on to see if it makes a difference, because that would indicate to me the boiler is indeed giving out too much heat. Trouble is though, what if I get the heat output reduced, then need all rads on because the kids are home for Christmas?
I was hoping there might have been something straightforward that I hadn't thought of but it looks like a job for a plumber. I shall try to get hold of the installer again, unless turning on all the rads solves the issue.

K

 

[Deejay]

Morning K

The boiler handbook gives some details on varying the heat output, but it involves fitting a different jet and re-setting the mixture which needs a gas analyser.

Is there a rotary knob anywhere on the front of the boiler? This would alter the flow temperature, whereas changing the jet will alter the maximum output.

Which boiler is it?

Cheers

Dave

 

[graduate_owner]

The boiler is a Grant Vortex Eco Utility 21-26.
The burner is a Riello RDB, and the attached plate says 1.6-2.8 hg / hr, and 19.2-33.5 kW.

There is indeed a dial on the front of the burner, which is fixed so that the edge is visible, and is currently set to 3. If looks like there is a screw slot beside it which may be the means of adjustment. I don't know if this can be adjusted without upsetting the burn mixture.

K

 

[Deejay]

Morning K

http://www.grantuk.com/wp-content/uploa ... r-2008.pdf

Have a look at page 4. It doesn't go into much detail, but it looks like the rotary knob turns the flow temperature up and down.

An infrared thermometer would be useful. You can get them on Amazon for as little as £9.

Cheers

Dave

 

[graduate_owner]

Dave, thanks for taking the time to scan those pages. The knob on page 4 is indeed the temperature control selector. The 'short cycling' still happens when this is adjusted, unfortunately. What I was wondering about is the adjuster which is on the lower right area of the boiler image on page 4. However I have been advised that this alters the air supply and so meddling with it will mess up the air to oil ratio but will not change the heat output. So from what I have learnt from the forum, and from Grant boilers, is it needs a different nozzle to reduce the heat output and so allow the heat to be carried away instead of building up too much. I'm guessing the plumber fitted a different nozzle when he serviced the boiler.

So I need to get the plumber back. Well that's fair enough, I don't mind that. It's just that I don't like forking out when the solution is a simple DIY job.
Thanks to all who offered advice - much appreciated folks.

K