Curious problem already stumped one plumber...

[Stoo75]

(Thread should say 'Curious Problem' not 'Curious Plumber'! Sorry)

I have a Baxi MegaFlo 28 HE boiler with an Albion unvented indirect cylinder in a pretty standard 1930's semi.

The problem, basically the Central Heating comes on for a while (maybe 30-45mins) then the boiler stops firing, however it comes back on when the hot water is active. It's enough to heat the house especially after a couple of baths as that seems to trigger the central heating. If the CH system has been off and is cold, clicking the override kicks it into action, after that nothing unless the hot water it on.

Observations:

The CH programme is on
The thermostat is on and calling for heat (up high to try to keep it going)
The motorised valve on the CH is open
The boiler has recently been serviced and seems to be working fine when it is initially on and also when heating the water in the cylinder.

Could it be the boiler tripping out somehow (i am totally ignorant on how they work) but i'm guessing there is some sensors in it that read the water temperature and fire up when the thermostat calls for heat?

It's driving me mad as i have can't seem to get to the bottom of it!

Any suggestions would be great, i am not planning on fixing this myself but would be good if i could point a plumber at the source of the problem without wasting anyones time.

Thanks in advance!

 

[lame plumber]

something sticking micro switch or rm stat etc, just get a decent heating tech to look.

 

[chris watkins]

Would you know if the pump is still running when the heating is off ? The boiler is likely to be over sized for your property do you know why such a large boiler has been installed ? (in condensing mode it is 30 kWs)
P.S. has it always been a problem or did it work correctly & now does not?

 

[tamz]

something sticking micro switch

Agree with LP here. Give the heating valve a kick or a hit with the implement of your choice. That should get it working again in the meantime but you will probably have to replace the valve head.

The boiler is likely to be over sized for your property do you know why such a large boiler has been installed ? (in condensing mode it is 30 kWs)

Very for a 1930's semi Chris unless it has had a 5 bedroom extension put on :smile:

 

[Dotty]

Thread title changed for you Stoo.

 

[CM25]

Does the ch 2 port stay open if u turn the ch off on prog? If so it's likely to be the that stuck open and coming on with hw then going off when the hw is satisfied

 

[prochoiceheatin]

Easiest thing to do is when its all gone off and stats are calling just check that there is a live coming back to the boiler. If there isnt its a component fault and not the boiler. Then check your valves at wiring centre are all supplying switch live for call.

 

[Stoo75]

Thanks for the info...

LP - is the microswitch in the motorised valve? One thing i did notice is when the heating came on for it's initial blast was the thermostat (set to the highest temp) switched off even though there was no way that it had reached 30° and i heard a ping and then the boiler stopped. The thermostat then lit up again but there was no response from the boiler, but the valve opened... does that narrow it down? If it was the microswitch wouldn't it not come on at all as it would fire up unless it got a signal from the microswitch?

Chris - the whole heating system was renewed when we had a loft conversion and was recommended incase we wanted to have an en-suite in the loft (couldn't afford it at the time, and still can't!) But everything had been working fine until the EV went in the boiler which has been replaced along with the safety valve on the boiler. We also had a constant leak through the tundish which lead to the inlet group being replaced... not great on a system that is only 2.5yrs old. Could any of this caused a further problem? I don't think the pump is still running, the boiler is silent and the water temperature display just drops to about 32 and stays there (unless it fires up for hot water).

CM25 - no the valve closes when the CH programme is off, so seems to be functioning properly.

LP - Would love to find a reliable honest heating tech, unfortunately had my fingers burnt with the last one, changed the EV and was supposed to change the inlet group but never came back, never answered my calls (unless i used a different number) just kept fobbing me off with empty promises, never gave me a receipt for the work. Ironically saw him the other day at a BBC DIY SOS big build project just around the corner obviously offering his time for free like some kind of saint!!! (rant over) Had to get another guy out to change the safety valve (which was dripping and was spotted by the dodgy guy but chose to do nothing about it) and the inlet group. Just feels like i'm throwing money at it and getting no results!

 

[CM25]

I think without being able to check with a multimeter in the wiring centre when the fault occurs it's going to be a difficult one to get to the bottom of as u need to know what voltage is going where (or not as the case maybe ;-))