Boiler lock out on going problems

[pete1001]

Hi

Any advice on a (still) unresolved problem that has so far seen five BG service call outs, a replacement thermistor(?), a new pump and new PCB, would be greatly appreciated.
I recently had a roomstat fitted on advice of BG. Until then relied on timer and TRVs. Had no problem until then but now the boiler regularly locks out; and makes nasty banging and whooshing noises as well. If I take the roomstat out of the equation (ie turn it to max) the problem goes away. From my observations the problem appears to come from the more frequent turn on / turn off that occurs with a roomstat but goes away when the on / off frequency is much less frequent (ie on all day and off all night). However, my CH knowledge is nil.
I can go back to just timer and TRVs but surely there must be a solution to this. I'm wondering if there is much more BG can replace!

Baxi 80HE Plus condensing boiler 3-4 years old (power flush at that time).
Honeywell T6360B roomstat.
15 rads all with TRVs fitted except one in bathroom.

Anyone come across this type of issue?

 

[TheGasMan26]

Sounds to me like no bypass, if its ok when your trv/s close then you've probly got 1 rad without a trv which acts as a bypass(ie-allows the water to keep flowing rather than stop dead causing overheat), if the roomstat is connected to a zone/3-port valve before your rads and the boiler has no internal bypass this could be your problem.

the solution would be to fit a bypass (a pipe from the flow to the return) simply under the boiler where all the pipes run into it, with a presssure differential valve (a valve that only opens when the pressure on the flow side increases over a set level, i.e-when the zone valve shuts due to roomstat being satisfied) thus allowing the system water to continue circulating around the bypass to dissipitate the heat rather than overheating(this can cause nasty noises) and locking out.

 

[Agile]

You could test this possibility by removing one of the TRV heads. ( Or probably just turn one up to max. )

Tony

 

[fitz1]

has any trvs been turned down since having room stat fitted.

 

[pete1001]

Thanks for the replies.

I have altered some of the valves and only the bathroom towel rail remains fully open constantly. This is new and was fitted at the same time as the stat. Could this be relevant?

I have put 2 TRVs on max to see if this improves the situation and i'll update in 24 hours.

It is noticeable that the close down process just sounds different when triggered by the stat to when triggered by the timer. Is it possible that the stat has been incorrectly installed? It was done by electrician so have discounted this.

More than happy to take advice re the bypass and pressure valve but need confidence that this will indeed resolve the problem before committing to the expense.

Thanks again for suggestions - really helpful.

 

[rojaca]

Hi Pete. No pump overun on this blr so unlikely to be by-pass assy' esp as Bathroom rad not trv'd. What are the Fault LED codes showing?
I would suggest Heat exch is blocking up. BG seem particularly unwilling to replace these regardless of the symptoms. (16 visits boys!)

 

[pete1001]

Hi rojaca - thanks for the interest.

LED fault is "overheat". Last BG engineer changed PCB because of what he called pump overrun (or lack of it). From what you say this was always destined to fail?

 

[rojaca]

The aluminium heat exchanger models do not utilise a pump overun- The pump can be wired to the blr but as the blr only works on a switch live once the feed is off, the blr and hence pump, are dead.

 

[HuwG]

Having not installed a Baxi for a few years, Im not sure. Is it a filter blocked maybe? Those ally heat ex's have incredibly small 'waterways' too, and are easily blocked. rojaca seems a dude who knows what he/she is on about. Are you able to determine the system your boiler heats.... Y or S plan. If unsure look it up.
Huw

 

[pete1001]

OK thanks. Sounds like I'm in it for the long haul with BG. I'll book another call out.

What was the reference to '16 visits boys' about? Did you have a similar experience.

 

[HuwG]

BG will get it right. Its a shame it takes them multiple visits to do it. I used to work for them, and was pulled in so many times in the early 90's for fixing boilers when they could be repaired. 15 years since Ive been on their payroll, and it seems nothing has changed.
Huw.

 

[rojaca]

Thanks for the complement Huw. Nope not really- Have you read the thread re "flow rates on heating- them boys know what they're doing!

16 visit's was the number of call BG had done on a Barcelona -essentially same blr- before calling us out. Took about 15 mins to get to the bottom of what was going on. A lot of the Heateam lads do these on the first visit (not me I'm not fast enough).

Sometimes guys will just change easy parts rather than commit to a fairly big task like this- this applies across the board and not just to BG

 

[pete1001]

Having not installed a Baxi for a few years, Im not sure. Is it a filter blocked maybe? Those ally heat ex's have incredibly small 'waterways' too, and are easily blocked. rojaca seems a dude who knows what he/she is on about. Are you able to determine the system your boiler heats.... Y or S plan. If unsure look it up.
Huw

Huw
Sorry just noticed your question. System appears to be Y plan looking at valve. One additional snippet is that the bathroom rad (no trv) heats up when either (or both) CH or HW on. Looks like a common return pipe has been used for the final stretch down to boiler. Could this be a factor? I guess this would act as a by pass if nothing else.

 

[Agile]

It would be quite clever to use a common return pipe to heat the towel rad if either the CH or HW was on.

I have never seen one like that though!

It would be more normal to connect the towel rail on the boiler flow but before the motirised valve(s).

Tony