Main boiler turning on and off despite reaching room stat temp

[Lee Robinson]

I have a Main boiler ( installation paperwork states Baxi Potterton solo 15HE ) however it looks similar bar the logo on the front.
Does this boiler have an internal thermostat? if so, I guess this could be the reason my room stat isn't reaching the required temperature at first before the boiler stops and then some time soon after fires back up and attempts to reach room temperature.

Then once it reaches room temperature it constantly starts and stops even though the temperature doesn't drop or rise. It could do this several times an hour.

I haven't had a boiler behave this way before. The last 15 years my previous boiler would stay on until room stat temp is reached then once it falls .5 or 1 degrees lower than desired temperature it would fire back up.

Is this normal for this type of boiler and should I be concerned.

Apart from that boiler works fine for Hot Water.
Thank you

 

[ianmcd]

all boilers have an internal thermostat which controls the burner depending on how it is set and what the temp of the water inside the boiler is, the thermostat on the wall cuts the boiler off when the room it is located in reaches the temp it is set to, the boiler internal thermostat is doing exactly what it is designed to do

 

[stem]

Ian is quite correct. Boilers usually produce more hot water that the radiators actually need, so if the boiler ran continually it would ...erm actually boil the water, which is something most definitely to be avoided, despite its name. The boiler thermostat therefore controls the burner to regulate the temperature of the water leaving the boiler.

Sometimes, older boilers particularly 'back boilers' were so uneconomical in that they lost so much heat up the chimney they tended to run for longer periods to make up for it.

 

[Lee Robinson]

Thankyou for your reply

Today I made a note of times and temp
7am - boiler has been off overnight and not fired up.

Boiler off - room temp 17'C
Room Stat increased to 20'C
Boiler on for 20 minutes - temp reached before it turns off 18.5'C ( would this indicate that boiler stat has reached its own temp? )
Boiler remains off for 2 minutes - Room Stat reading at end of period 19'C
Boiler remains on for 1 minutes 25 seconds - Room Stat reading 19'C
Boiler remains off for 4 minutes 19 seconds - Room Stat reading 20'C
Boiler remains on for 0 minutes 25 seconds - Room Stat reading 20'C
Boiler remains off for 2 minutes 48 seconds - Room Stat reading 20'C
Boiler remains on for 1 minute 40 seconds - Room Stat reading 20'C
Boiler remains off for 4 minutes 05 seconds - Room Stat reading 20'C
Boiler remains on for 6 minutes 06 seconds - Rooms Stat reading 19'C
Boiler remains off for 4 minutes 22 seconds - Room Stat reading 19'C
Boiler remains on for 1 minute 48 seconds - Room Stat reading 19'C

Based on the replies, I guess this is how I should expect this CH system to work?
This doesn't appear an economical way to heat my home. The radiators get home but not enough time to remain heated by the boiler to heat the house.

 

[jackthom]

There isn’t a water temperature gauge on the boiler but how high has the control on the front been set and do the radiators get hot to the touch?
During this on/off switching of the boiler, if the radiators remain hot then the boiler is doing it’s job and it just means it probably can’t wind down the gas flame low enough to avoid overheating the water.

 

[Harry Bloomfield]

I have a Main boiler ( installation paperwork states Baxi Potterton solo 15HE )

That boiler would seem to be a very basic condensing boiler, with no ability to reduce its Kw output level, so it's all or nothing. All it can do, if it hits the preset temperature set on the front panel of the boiler, is shut down until it cools down a little. So on/off firing is to be expected when ever there is a demand for heat.

 

[Lee Robinson]

There isn’t a water temperature gauge on the boiler but how high has the control on the front been set and do the radiators get hot to the touch?
During this on/off switching of the boiler, if the radiators remain hot then the boiler is doing it’s job and it just means it probably can’t wind down the gas flame low enough to avoid overheating the water.

I will check out the temperature setting - thanks for suggesting
All radiators get hot, they were balanced by CH engineer after some of them were not getting hot, so I'm happy with that being set correctly.
The radiators seem to remain hot throughout as the boiler is as quoted switching on and off.

 

[Lee Robinson]

I have taken a look at front of boiler. The temperate dial is as far clockwise as it can go. I assume this means the temperature the boiler can create is high or as high as it can go. Is there any merit in turning this down? Will this allow the boiler to stay on longer pushing heat to the radiators and allowing the room stat to have a greater say in how warm the room should be?
Or will this be counter productive.
This boiler claims to be high efficiency rated but I can't see that myself if every few minutes it's firing up then stopping and repeating this constantly.

 

[Gasguru]

Those boilers are a 25 year old design inside...what's known as the turndown ratio (the maximum output versus the minimum output) is very poor by todays standards..around 9kW at the minimum.
That means that it will cycle on/off once the flow pipe temperature has reached around 80 degrees (the highest setting on the boiler thermostat) and the 9kW heat energy can no longer be dissipated.

 

[Lee Robinson]

Thank you to everyone who has posted on here. It's all much clearer and guess the issue is whether I invest in a new boiler?
Old maybe less economical boiler for next 10 years or replace at a cost with much more efficient and modern way of operating!!
Any suggestions on what would be a good investment for minimum 10 years. No doubt the whoever I get will suggest a make and model of boiler that they like or they fir often.
I live in 4 bed detached home.
1 Bathroom
1 Onsuite
1 WC
Also I have 15 radiators and 1 towel rail.
CH engineer said this 15Kw boiler isn't really man enough for the job in a house this size with this many radiators. I've only been here for 5 weeks and already realising this 5 year old installed boiler wasn't the right choice for the previous owner.
Any suggestions on what I might be looking to go for.
Boiler is in the kitchen behind wall unit enclosure
I have water tank and loft header tank
Would it be as wise to keep with this format and just replace the boiler ( simple replacement in situ ) or would a combination boiler be the way forward. I guess the combi boiler would then cost more to install as it would require different work to install?

 

[dal5band]

You need to check what your room thermostat is controlling. With the room temp reached as set, the thermostat should switch the boiler off , provided the hot water is also up to temperature. Seems your room thermostat is just controlling the pump, as this was the setup invery old systems - the boiler keeps cycling on/off in accordance with its water thermostat but the water is not circulating because the pump is off.

 

[Lee Robinson]

You need to check what your room thermostat is controlling. With the room temp reached as set, the thermostat should switch the boiler off , provided the hot water is also up to temperature. Seems your room thermostat is just controlling the pump, as this was the setup invery old systems - the boiler keeps cycling on/off in accordance with its water thermostat but the water is not circulating because the pump is off.

Thanks for the information.
I have drawn a diagram of wires in my cupboard where the valve, pump, cyl stat is.
I have two cables coming in
One cable with 2 blacks, 1 G/Y, 1 Brown, 1 Blue
One cable with 1 red and 1 black.
I can trace them so far as seen on my diagram.
The red cable coming in appears to come from my old wall stat, so I have joined them together. If I didn't then room stat (TR6) didn't have any control or ability to switch on and off. So cable from terminal B on TR6 goes to the valve.

 

[dal5band]

I think that's as far as we can go : if the cylinder stat and the room stat are both turned down, the boiler should be off. If the boiler keeps recycling with the thermostats off then your system is wired differently. Get a CH electrician.

 

[Lee Robinson]

Thank you for all your help.
Electrician booked