halstead finest gold switching on and off dhw

[lonner]

sorry for a long post but ive tried to give as much info as poss

Right ill tell you what i know and what has been done etc.

problem = boiler works fine on heating but switches on-off during dhw demand.

ive changed both thermistors.

ive checked the switches on the diverter valve work and there bone dry and both work as they should.
fitted new diaphragm etc last year.

i have fitted a secondhand pcb which is ok and the problem is exactly the same with the new one so pcb ok.

had a long chat with halstead technical to no avail

venturi ok no blockage.

the water temp is nice and hot when working and flow is perfect.

i can get the dhw to run better if i turn the temp down but it still does it intermittently.

the boiler does not lock out!!

it just cycles and restarts runs for 20secs and off and starts again.

this problem is a sod and i cant get any info on a fix or reason.

there seems to be some very knowledgeable heating engineers on this site so thought id see if you had any thoughts.


ps i run a hard landscaping business so ill return the favor if you need any help with the garden or drive if thermo dont beet me to it


thanks for any help

 

[slapper]

Well, I would look at a partially blocked heat exchanger as the next step

 

[lonner]

thanks for your reply
have thought this may be the case as its been mentioned on other halstead issues(there is a few with halstead)

Well, I would look at a partially blocked heat exchanger as the next step

take it you mean the dhw plate one at the base of the boiler.

it does deliver a perfect flow of water but if its partially blocked it would cause the heat at the thermistor to be high as its restricting the flow.

i have a spare thermistor so would connecting it to the plug then putting it in an egg cup with a little hot water in it fool the boiler and thus expose the heat plate problem

is that a good thing to try

 

[lonner]

good diagnosis slapper

the heat exchanger was partially blocked with lumps of scale.
i cleaned it out and now it flows well and another thing i noticed is the cold fill now only takes a few seconds to pressure up the boiler instead of ages so there was a restriction.

thanks for your help.

surprised halstead couldn't help or advise on this prob as its not uncommon

 

[yoshimura]

I have this exact same problem,- looks like i gotta do the same thing any tips //www.diynot.com/forums/viewtopic.php?t=209995