Boiler cutting out before CH temp reached

[Irie]

Hi, I'm having a problem whereby the boiler turns itself off before the temp has reached the setting on the room thermostat. I'm sure there was a time when it would keep going until the termostat temp is reached!

We've had a powerflush done, I've balanced the rads and we have had the boiler serviced (with some new bits chucked in due to intermittant firing). Could this be a problem with the boiler or perhaps with the pump / 3 way valve?

This sort of follows on from my previous thread: //www.diynot.com/diy/threads/myson-mpe322-rest-position.447506/

 

[stem]

Depends on your boiler. But with older boilers, the boiler thermostat controls the temperature of the water leaving the boiler, and will turn the burner 'on' and 'off' to maintain the selected temperature. Despite it's name, the one thing a boiler shouldn't do is boil the water.

However, most boilers are oversized for the capacity of the radiators connected to them and so will turn on and off frequently. So what you describe sounds perfectly normal to me. In fact I would be worried if it kept going.

Newer boilers are 'self modulating' and the burner adjusts the size of the flame to provide the heat required, but from your descriptions it would suggest this is not what you have.

 

[Irie]

It's a Potterton Promax 15 HE Condensing boiler. The only problem is, the rooms are simply not getting warm enough! I've currently got all TRVs fully up, thermostat set to 30 and nothings happening.

 

[gasmanstu72]

the thermostat on the boiler governs the temperature in the boiler that is pumped around the radiators,
the room thermostat governs the air temperature in the room that it's in.

its normal that the boiler cuts off before the room reaches temperature,
are the radiators all piping hot but the room is cold? could be that the rads aren't big enough for the room

 

[Irie]

Right now the rads a pretty cool. I've just hit the reset on the boiler and it immediately came back on. Methinks it might be a boiler issue and needs the engineer back out... After 4 visits I had hoped today's fix was it as everything seemed fine!

 

[Agile]

So what were all these four engineer's visits for then?

Why not tell us the whole story at the beginning?

Tony

 

[mcmoby69]

Hi, I'm having a problem whereby the boiler turns itself off before the temp has reached the setting on the room thermostat. I'm sure there was a time when it would keep going until the termostat temp is reached!

We've had a powerflush done, I've balanced the rads and we have had the boiler serviced (with some new bits chucked in due to intermittant firing). Could this be a problem with the boiler or perhaps with the pump / 3 way valve?

This sort of follows on from my previous thread: //www.diynot.com/diy/threads/myson-mpe322-rest-position.447506/

who decided that a powerflush was needed?
you balanced the rads...... how many systems have you balanced before?how can you balance a CH system that is not working correctly?
had the boiler serviced? (what to correct a circulation issue?)

i think you need to start again with a decent heating engineer.

 

[Irie]

So, we started off with the powerflush - it had been recommended when the boiler was serviced previously but we never got around to it but this last autumn I wanted to get it sorted. I'm no expert, but think I got the rads balanced alright, everything seemed fine. Then I noticed the system wasn't behaving quite as I expected, not quite getting warm enough etc.

Then we had our annual service completed a few weeks back. The next day the boiler didn't fire up, luckily we are on a service contract. Flicking the reset switch would spark it into life for a random period of time. Diagnosis was new combustion door + seals (though on this boiler I'm under the impression best practice is to replace the seals every time the boiler is serviced...) and new electrodes. After a delay, it was all fitted the following week. The engineer also said the gas flow was too high and adjusted accordingly. Engineer left and all seemed fine. Fast forward an hour or so and the boiler was making a horrific noise so called him back and he diagnosed needing to adjust the gas value to account for the new flow rate. Turns out the adjustment head was knackered from a previous engineer (prior to us buying the house I would hope as as far as I'm aware, out first service didn't need any adjustments) so we needed a new gas valve. This was installed on Friday, everything all good... Nope, boiled didn't fire up again on Saturday morning. Had engineer out again the morning who diagnosed a fauly ignition PCB. Hopefully the new PCB will cure the issue...

 

[mcmoby69]

Did the bloke who did the powerflush remove the pump and connect there or somewhere else.?
I reckon the pump is clogged up.
Had one similar a couple of weeks ago.

 

[Irie]

Seems like the PCB was the issue - this has been replaced and the boiler is working much better. Thanks for all the input.

Did the bloke who did the powerflush remove the pump and connect there or somewhere else.?
I reckon the pump is clogged up.
Had one similar a couple of weeks ago.

He connected it to where the pump was I think. The pump is a little scaled, and might get replaced later this year

 

[JBR]

This may not be relevant to the OP's problem, but I though I'd mention what happens with my boiler and room thermostat.
The thermostat is set to 20 degrees and the flame indicator actually goes out when the temperature reaches 19.5 degrees. Although the boiler is no longer heating the water, the radiators continue to give out heat until the room temperature reaches 20 degrees (or actually a little more). In practice, the room temperature remains at round about 20 degrees.
I think this is a common situation.