Yet another Baxi Solo 2 50PF overheating problem...

[judas123]

Hi, I recently bought a two-bedroom house which has a Baxi Solo 2 50PF boiler in the garage, Drayton Lifestyle LP522 controller in downstairs wc, a large hot water tank in the loft, 4 radiators (one without temperature control in the downstairs hall - presuming this is the main one? the rest with controls), and a heated towel rail in the bathroom upstairs, which has a temperature control.

Being a first-time buyer I was advised by my solicitor to get the central heating system checked no later than 5 days before date of entry, for which I enlisted the services of a local gas and heating engineer. He checked the system and declared it in perfect working order, of approximately 8-10 years old, and a british gas installation of good quality.

Upon entry date I moved in and the previous occupiers mentioned as they left "sometimes the boiler needs reset, just turn this knob round to 0 and back round, we've had it checked by various folk and they can't find anything wrong with it, but it only does it sometimes"

I think their definition of sometimes differs from most peoples... every day without fail at least once it will lockout with the overheat light lit and require reset. I got the guy who checked it back to have a look, he denied that he missed anything in his check of the system and was assured by the previous occupant that the the system worked perfectly - seeing as the missives stated that they were not responsible for any repairs costing less than £250 I was not unduly worried because he had stated it was in good order, figuring that it would work as expected.

In attempting to rectify this fault he has replaced part after part, without testing pieces before replacement.

So far I've had the following replaced at my expense...

• 
  Pump
  Overheat Thermostat
  Thermostat Sensor
  Automatic air vents fitted to tank in place of manual ones, and an automatic vent fitted to the boiler "as there wasn't any before and there should have been"
  Boiler temperature control potentiometer

It only seems to go to overheat when the central heating system is on, hot water only does not seem to trigger it. I tried turning off all the radiators and towel rail apart from the main hall one which doesnt have a temperature control knob - it lasted for 2 days before kicking to overheat, which is an improvement, but a chilly experiment.

The boiler doesn't seem to make any strange noises like banging or clunking (apart from the light ticking noise when cooling down - I put this down to thermal expansion), but it does click on and off when operating - fires up for a few minutes, then off again for a couple of minutes, then on again - don't know if this is by design. All radiators get nice and hot, and the water gets hot too. I have the room stat set at 20c, the danfoss stat below the boiler set at 55c and the hot water tank in the loft set at 55c. The valves move as expected, the pipes and pump get hot.

Any suggestions as to what to try next? I had suggested following the forums on here to him that it may be the PCB board, but he won't fit one for testing and remove if it doesn't make any difference, and I don't want to buy one unless it's almost guaranteed to be that.

I sought a second opinion, engineer #2 who is difficult to get hold of and seems to be less than reliable at turning up when he says he will says that from my description (he hasn't seen the boiler yet) that half those parts shouldn't have been replaced, it won't be the pcb, but probably a blockage somewhere - is there anything I can do myself to check for that?

I have the installation and servicing manual for the baxi if it helps with part numbers etc, but as you can probably tell I am a complete novice with central heating systems so please be gentle with me!

 

[chapeau]

My advice would be to get British Gas in to take a look, think they do a one off boiler repair fixed price deal. Don't bother with the local one/two man bands when you get these sorts of problems.

 

[swbjackson]

My first thought is that the boiler is oversized for the system. The boiler needs to be rated at it's lowest output. Make sure the pump is connected through the boiler so it can over run.

Do you know what control system you have? Is it an S plan (two zone valves) or a Y plan (1 mid position valve)?

British gas will probably come in and tell you that the boiler is obsolete and the system needs flushing.

 

[judas123]

Thanks, I think it's an S-plan system, as it has two motorised valves, one for hot water, and another for central heating. They are on seperate pipes which then join together into one, which then goes into the pump and then into the boiler.

Probably some pictures would help, I'll take some today to show what I'm on about.

 

[chapeau]

British gas will probably come in and tell you that the boiler is obsolete and the system needs flushing.

Well then you have two choices.

1) Pay for new boiler and system flush
2) Say thanks for your free advice and go elsewhere.

Or

3) They fix it at a fixed price and guarantee for 12 months.

That's what they did for me when my exact same boiler stopped working a couple of years ago. It had been improperly installed by the Corgi engineer, and several local Corgi engineers failed to notice this and just replaced expensive parts which naturally didn't solve the problem.

And at least BG turn up when they say they will.

 

[picasso]

post up some pics so we can see if there is a bypass fitted.

 

[DP]

Chapeau

And at least BG turn up when they say they will.

What are you on about? A handyman will turn up on the dot. A heating man with NO JOBS will turn up on time. A good engineer will turn up around the time specified or will call and say he is delayed. Who would you prefer- a general dogsbody who will throw parts at the boiler or a person who turns up 'eventually' and crack just about any fault on a boiler and ONLY changes part that is defective- even tell you there is no part need and boiler needed to be set correctly

What makes you think the system needs power flushed?

I can do a fixed price repair (£1000) for just about any job, but is the price going to be right? And, all my jobs are guaranteed for 12 months with margine if the system fails 'just beyond' the 12 months like often happens in life.

 

[matt1e]

post up some pics so we can see if there is a bypass fitted.

as above and also check that the pump does actually run on after the call for heat is removed

it does click on and off when operating- fires up for a few minutes, then off again for a couple of minutes, then on again

then either you have a circulation problem or more than likey the boiler's over sized as swbjackson has stated

Matt

[/quote]

 

[petit_pablo]

Bet its the pump relay on the board

 

[sandybeach]

post up some pics so we can see if there is a bypass fitted.

Agreed. The Solo 2 requires an 8 meter by-pass for the pump over run, piped in 22mm. If the by-pass ain't there or inadequate then thats your problem.

 

[Baxmax]

I suppose an answer to the question "is the pump wired back to the boiler" would get the ball rolling

 

[judas123]

Photos as promised, if there are any close-ups or other photos required please ask, I've included the radiators and towel rail anyway in case they're relevant with regard to size.

//www.diynot.com/network/judas123/albums/12710

Thanks for everyones input so far

 

[judas123]

p.s. the pump does run on for a number of minutes after the call for heat or water has ended, it's usually after the call has ended that the overheat light clicks on, i haven't seen it do overheat while it's actually running...

 

[swbjackson]

Looks like it's got the good old gate valve bypass fitted. I'd be getting shot of that and fitting an auto bypass to start with. At the same time you can check the state of the water in the system.

 

[judas123]

thanks, is the bypass gate valve the bit with the red wheel?

what would i be looking to see in the water - rusty colour/floating bits etc? The water comes out clean from the taps, but i'm guessing that's completely seperate?