rads not heating - ravenheat rsf82 - trv problem -weird one!

Evening all,

Im having a spot of bother getting 6 trv's to behave on my rsf82et combi system.

My tenants have had the trv's on full for ages and ive just learnt that theyve been taking the heads off, pushing the pins down then replacing, back on maximum. apparantly, the rads have only been working if the trvs are on full.

Boiler runs fine, then cycles (one minute on/one minute off) as though its reached temperature...but it hasnt...oh, by the way, theres no room stat, just basic stat on boiler panel. I dont think its flame rectification as it does fire up for a while from cold, i dont think its the thermistor as the boiler doesnt kettle and then shut down...it appears to run fine...just cycling too much.

I took heads off trvs myself and freed the pins off with a bit of silicone grease but this seems to have made it worse! Rads/water are in fairly good condition and its all 15mm pipework.

I dont think its a balancing problem as the system has worked fine for years.

Would all 6 trvs play up at the same time? hmmmm...although they dont exactly feel to be moving smoothly (almost as if they want to turn closed?)

My fear is that its the boiler stat caused by excessive use (by process of elimination), which would probably mean a new pcb...

Or could it be the thermistor going mad, thinking its too hot and knocking the boiler off?

or am i missing anything???

do the rads get hot at all...or warm?

thats the thing...

theyre all slightly different...half get warm...the rest struggle.

I cant get the boiler lit long enough to see if the rads heat up fully.
But the boiler seems ok, as though its a system fault?

does boiler stay on for hw? can`t imagine all trv`s faulty at same time........ thermistors can cause loads of problems on ravenheaps... htg thermistor faults usually cause problems on the hw side too though....

ill have to try the hot water tomorrow...they didnt mention any problems though..and i never thought to test it!

i know about the thermistor problems on these...but thought if they were playing up, then the modulation would be all over the place and starting to overheat/kettle? or can they be more subtle? which would explain the cycling i suppose?

just say that the water is ok though!

what else can i check/adjust while im there?

Just while im on...theyve always had the boiler stat on half(ish) and its worked fine...now its on full and causing bother...could it be the boiler stat/potentiometer?

this one has fried my head!

in my experiance thermistor faults usually cause faults like not even firing up,( pump only).....intermittant htg and hw...on/off on/off faults...... etc.... is boiler kettling? maybe needs a clean out.....? does flow get hot as it should....maybe DV stuck...? all i can think off at moment. let us know tomorrow evening if u got it sorted or not...

CC? CCC

The thermistor could be going open circuit and shutting the boiler off but only when warm. Its less likely but easily checkable by substituting a fixed 22k resistor for the thermister on test and see if it stays on.

There is a problem with cycling on that model. All those that I have encountered dont have any anticycle delay and over cycle. I did ask at Ravenheat and was told that a few were getting sent out with anticycle disabled. I think I was told how to enable it but if so then I dont remember. No customer has ever complained or wanted to pay me to investigate it. Just something I have noticed on performance tests during gas safety checks.

You also need to measure the flow temp at the boiler at the point when it goes off but the thermistor substitution test will tell us a lot.

Dont assume your tenants have not adjusted the lockshields!

Tony

Before looking at the boiler, I would have to be satisfied that the TRV's are definately in the open position and that the L/shields are open as well and not partially bocked with dirt, some Danfoss TRV's are notorious for sticking shut.

assured heating, Agile and PEDANTICVINDICTIVEMAN

Don't you look at the posting date? This topic last had any activity on Wed Jan 20, 2010. I think your replies may have missed the boat.

I did look at the posting date but only as far as being 2010 !

Thats rare for me to miss the full date but I have an excuse as I am upset at seeing my stolen car being towed past me by gipsies as I was on my way to renew the tax and having to deal with the Police who were unhelpful in the extreme.

Tony